@Kouga
This is an incredibly well written post. Despite its length, it doesn't ramble and it's very straight to the point with sound reasoning. I'm going to be as thorough in my response as I possibly can be and if I miss something, please point it out.
A good chunk of my post is very broad in nature. Not because I want to intentionally dis-include anything but because the nature of my belief behind this has an extreme depth to it that takes quite a bit of time and effort to explore - to be quite honest with you, I doubt most people are interested in reading that. But because you brought it up, I'll explain.
When I say game knowledge, this excludes very basic concepts of the game that any average level 30 player should have. Game knowledge isn't exactly a stat that can be measured, the higher the elo, the higher level the play is. The higher the level the play, the more complex the game becomes at a very minute level. While a lot of basics are still shared between all elos, as I've noted, it gets a bit more complex.
So when I make this statement, I make it on the backbone that there's no way a silver player can understand how to play in a diamond game. The diamond game will be much more punishing of mistakes, even the smallest positional mistakes that are often made and left unpunished in low elo. The game and the decision making are played at a much faster level. Snowballing is much harder because people know how to punish mistakes harder. While some of this is true in all elos but to a lesser and lower quality of play, as its higher, and I hate to wear this word out, it's more complex and in depth. Simply put: there's no way a lower elo player could ever understand this. The only way they do is by ranking up and experiencing it.
I'll give you an example I like using to describe this. Imagine you're watching a front page game of ranked high elo. You see a Hecarim and Darius fighting it out. Darius is running flash/ignite, Hecarim is running ignite/TP. You watch as the Darius has Hecarim under tower and below half health but Darius is barely above half himself. Darius hits six with just a few of his minions left dying under tower. Many low elo players would probably wonder why Darius isn't walking up to the escapeless Hecarim and dropping a Q/AA/R/Ignite to secure what seems like an easy kill. Instead, the Darius backs. How many people will understand why he backed instead of securing what seems like a sure kill?
Because a few things: the minion wave is going to reset in the middle of the wave after those minions die, or damn close to Hecs tower. Darius has it warded but doesn't see the jungler, he can only assume he's nearby expecting the dive. Darius would most assuredly die as well as he would draw aggro and Hecarim would likely ult him under tower. Darius has flash/ignite, not TP. So if Darius secures the kill and you'd think "snowball champion so it's a win for him," it's not. Hecarim is just going to TP back in, freeze the wave as Darius is going to be denied minions since his minions will be right under Hecs tower. They still traded 1 for 1 so Hec got a good chunk of gold and because of the freeze, Hec is going to be last hitting more and will also gain an EXP advantage to boot. Not to mention, Darius typically doesn't want to blow flash unless it's for a kill that doesn't involve his own death because of how easy he is to gank, he basically wants to have flash for straight forward sure fired kills or an escape.
In this situation, I can promise you lower elos wouldn't consider half of this and go for the dive. This is an example of small details you must always pay attention to at all times of the game. And not only must you pay attention, you must understand what's going to happen next and predict it accurately. At lower levels, this in depth knowledge and thinking just doesn't happen. And that's why I say there's no way they have the same knowledge. They may be knowledgable of the game, but understanding so many small things that a high elo player does likely just doesn't happen because they've never had to think this way and very few players, if any at all, can put a lot of this shit into words.
What impact does this have on balance knowledge? A pretty big one. Because some champions, as a result of less knowledge and in depth thinking, can take complete advantage of this due to the natures of their kits. So as a result, from the above example, that Darius in silver would likely dive the Hecarim and die and lose ultimately in the end because that kill was actually a bad trade for him. The first thing he'd do is QQ "omg Hecarim so op I dove him killed him solo but he just farmed and outscaled me."
Hecarim might actually be op, but because of his inability to rationalize this as a mistake and blaming the champions, he actually doesn't improve. And if he were to instead focus on what he did wrong, what caused the bad trade on something that seemingly seemed good, he just got better. And over the course of time, he's going to learn more and more about the game in small intricacies because of that. So eventually, he just won't be low elo anymore. Is that to say every low elo isn't in the process of that learning experience right now? Absolutely not, but a deep understanding is still rather lacking if they're still in low elo. That's just a matter of time for them, not a matter of if.
So when I think elo, I don't actually think rank as skill. I see it as a measurement of the players ability to approve, adapt, learn and climb. Though it is skill involved, I see that skill becomes a secondary byproduct of the climb and knowledge, experience is what's likely gained first and most probably noticed by the player right away, even if subconsciously. Combine this with the above written paragraphs, and sorry, there's just no way a low elo player has the same knowledge. Not because they're stupid, not because they're incapable but because its just a matter of not experiencing the same things that higher level of play demands.
Now, regarding mechanics. Mechanics are absolutely important. But I truly believe mechanics require a lower threshold of skill to raise in elo than knowledge does - that's not to say there's extremely gifted but less than average knowledgable mechanical Players in high el because there are. But it's a rarity. So much of this game is decide on the decisions you make from all points of the game, as long you have the bare minimum set of mechanics required to compete at your elo, you can win - it might take longer to grind up than others but you should win. As I stated, after a certain point, I don't think you can get away with poor game knowledge doing this. And as I said in my OP, I do believe there is a certain threshold in very high elo where you have to have some damn good mechanics if you want to continue to rise.
But all this said, I will absolutely never dismiss the statements of a lower elo player just because they're lower elo. The only time I would is if they compare their games to mine and assume we see the same things - I spent quite a bit of time explaining why they don't so I believe that's clear why id mention elo at that point. And there are times, probably more common than some low elo players would like to admit, where I can read their statements and just dismiss it as low elo ranting because that shit doesn't fly in high elo. An example would be the spammed usuage of "focusing the tank." Focusing the tank is bad when your entire team blows it's load on an ulted Alistar after his combo is down or a Leona with W active while her combo is down. Focusing a ghosted Nasus, while built tanky, isn't "focusing the tank." It's focusing the biggest fucking threat to your backline and likely the enemy teams tankiesst member and largest source of damage aside from the ADC. Yes he's tanky but he's immobile and can't just walk past front lines. Applying minimal CC on him and kiting him easily kills him, and kiting him as a team more importantly since the burden is on him as an immobile melee champion to get to your back line, is not focusing the tank. Anyone who says "yeah ok focus nasus, just focus the tank. Good job on losing the fight because you focused the tank." When I see that, I just dismiss it - any high elo player would know exactly what i just explained to be true because in high elo, Nasus isn't really a problem in teamfights - he's easily dealt with. And this is just one of many examples I can name as something I'd see from low elo ranting and banter that I'm simply going to ignore and dismiss.
But again, i will never dismiss a players statements just because of their elo alone. if it has sound reasoning, logic, respectable knowledge behind it then I have something worth discussing. When it's just angry downvote one line spammers mad because the truth hurts, there's not much I can do.
So if you get upset about this but you are trying to learn the game and improve your knowledge, know that the low elo banter and low elo mindset doesn't apply to you - because over a course of time you will just get better. And your knowledge will improve and expand as a result. Just know that it never ends, even at the highest of elos, knowledge and the expansion of it is ever growing. Even at the pro level this is true because the game is ever changing. So keep grinding and you'll get there.
As for your rank, frankly it's hard to say. Unranked players can be an enigma. In some cases, they can be pretty damn good but in reality, there's no credentials backing their statements if it comes down to anecdotal evidence. But that's about it. Again, if you have solid reasoning and a presentable argument, that's something that can be discussed and elo or lack thereof should only apply to a minimal level.
I hope this covers your questions. I haven't had to think like this or lay out my thoughts like this in a long time and it's really refreshing to do so, so thank you for that. Again, if I missed something or it's unclear, ask away and I'll address it or clarify.