At the end of the day, everyone up through Diamond is pretty garbage at the game (though in Diamond you'll commonly encounter many Master tier or Challenger players on their smurfs), they're better mechanically, and usually decision making wise as well.
But, as for game knowledge (what to prioritize, when to go for it, when not to, when does my enemy spike, when do I, what are my win conditions, what are their's?) they are usually quite lacking.
Most Diamond junglers I've encountered (not all), do not properly rotate for a Rift Herald (especially when it is free, uncontested, and there is nothing else on the map to take or do; i.e. no major waves pushing and no real ability to take a tower or an important dragon is up), so you'll often see them do weird things as if they were in the lower elos just as much as the Bronze/Silver junglers. Now, on the other hand they are often better at ganking, creating ganks from nothing, making good picks, properly smiting, doing proper and efficient jungle clears, and do tend to help their laner's shove out a wave and then back safely after a successful gank (to continue to deny the enemy laner).
Around Bronze is where people are totally incompetent, they do not understand how to play the game at all really, not for the most part. Silver they usually understand a bit more about the game, and can play their champions moderately efficiently, but lack true skill or expertise in any particular role or champion, and likewise are not playing any champion to it's standard capacity. Gold is where we see people being competent with their champions and roles, they can typically play a single champion or a few well, but are extremely limited beyond that and struggle to understand and learn different matchups, playstyles, or roles (and therefore how to counter them). They will usually be capable of playing the baseline champion (using their abilities correctly for example), but typically lack the necessary knowledge on how to abuse their advantages and mistakes of the opponent to win hard. Plat is the middle between Gold and Diamond, of which relatively few can successfully climb out of, in particular if a person maining a specific champion or role does not quickly climb, it is unlikely that they will ever leave that rank or it's general vicinity. Mistakes matter a lot more in Plat elo, people are typically capable of exploiting the weaknesses and mistakes of their opponent moreso than before, and counter picks are all the more stronger and important as a result. Someone who has played thousands of games on the same champion, but are unable to climb (I've seen it) will continually make the same mistakes over and over again. Their ego gets in the way, and they refuse to admit what they're doing wrong. Diamond players are usually some of the best players in the game, but are very much overshadowed by their peers in Masters or Challenger. Those who reach this rank usually do so by a few champions, and have the ability to recognize mistakes while developing new skills and strategies to deal with opponents. Their expertise in one role is greatly eclipsed by their severe ignorance or basic inability to play other roles at or beyond a Gold level (Imaqtpie trying to play toplane for example; he is a Challenger Player, but would be unlikely to hit beyond Plat as a toplaner, if he could hit Plat). PantsAreDragon for example, when put into the bottom lane, was incapable of properly executing his early game, exploiting the strengths of his role or champion and imposing upon his enemy for their weaknesses. BoxBox was put into the ADC role, and completely incapable of determining a basic Caitlyn build, or keeping up with changes that have occurred within the last 6 months on the champion that shifted her build significantly. His positioning was horrid, and ultimately he lost his team the game by getting caught out, while severely out of position, in the enemy Jungle, attempting to surprise the enemy ADC or Support. These are all good or great players, and yet their ability to excel in one area, is overshadowed by their severe weaknesses in other roles or champions.
It's ultimately up to you where you end up, but you have to understand what realistic limits are (a third of the player base goes beyond Silver, an extremely minuscule amount hit Plat, even fewer hit Diamond, and an extreme minority take it further to Masters and Challenger ranks), and understand that for the majority of people, it's unfeasible to even hit Gold. You could probably reach it temporarily by abusing something like Sona support every match, but know that something like that won't keep your rank stable, at the end of the day, next patch when Ardent is nerfed into the ground, and supports start becoming reasonable again, you'll just drop back in elo. And people that think they deserve Gold, but are stuck in Bronze or Silver will likely never reach Gold until they become much, much better at the game. It's how far you are willing to push yourself that matters the most at the end of the day.
vs 
or something close to it nearly every game? Why would I want to rank up, only to have to deal with people sitting botlane the entire game trying to get theirs the items they need to carry?
mid but if you're a high dia player vs another high dia player, 
because they're playing champions at their fullest potential. The meta will favor 
