The absolute worst place to play in this game is Plat V. Admittedly, I've never played in Diamond or higher (although I've watched friends that are at that level many times).
Plat V has a few problems...
- MMR boosted accounts are EVERYWHERE. It's painfully obvious when you look at someone's match history and they have won 30 out of their last 35 games with enormous K/D/As, great CS and utter domination over the opponents on a specific champion/role and then suddenly when they hit Plat V, they don't play that champion anymore, their CS is at Bronze/low Silver level and their gameplay (which is easily the most telling) shows a lack of knowledge and positioning, their mechanics are not Plat level either. There is also the other obvious signs such as different summoner spells on different keys, etc.
The obvious skill disparity in Plat V games stems almost entirely from this. I'd put account sharing or people that sold their Plat accounts to others into this category as well, but I don't think that's nearly as pervasive an issue.
-
Everyone is a hero. There are some legitimately good players in Plat V, some of them are likely to keep climbing, but they have one small problem... they think they're already Challenger material. I remember a game in which our Quinn top had a huge advantage in CS and kills, something along the lines of 50 cs and 4 or 5 kills ahead of their opponent at about the 10-11 minute mark... she roamed into the enemy jungle and killed the jungler, went mid, got a kill there, etc. So now, she thinks she's invincible... decides to 1v3 and gets blown up while taking only one of them with her. This happens quite a bit in games, but then later in the game they continue to think they're lead makes them unstoppable and that they can freely push or take on 3-4 at once. Getting caught out late game is just a formula for either a free baron or the end of the game.
-
General Complacency. Some people had a goal to get to Plat V, and they did... so now they're just happy to be there and go through the motions of a game. They do what they want, they play how they want and don't really care, they figure that if they get back to 0 LP they'll turn the 'tryhard' back on and avoid demotion, but they're not going to make any effort to climb and they freely admit it. This is a bit less common than the others, but I've seen it.
--
Bronze and Silver have their issues, there's no question, but some of those issues never go away no matter how far you climb. There are some people that just never want to group or fight with the team... Silver is, by far, the worst for this problem. Gold has people that have MMR boosted to that level as well (presumably for the reward of the gold border and victorious skin), but I still think it's worse in Plat, mainly because the skill difference is even more apparent at that level than it is in Gold.