Every ELO is bad. The issue with Platinum, much akin to mid to low Diamond is that the players despite being bad, have it in their heads that because they're at that ELO they're good. So they tend to not accept any criticism yet they still make stupid mistakes like building damage despite having lost their lane hard, or are in process of losing lane.
The issue is more that Riot has forced the game to be more team oriented which makes it cancer, at least in previous seasons like season 2 or 3 if you were really good you could usually carry the four idiots on your team. Now solo carrying isn't exactly as doable, it's still possible but it's a lot harder to do unless you're either experienced doing it often, or the enemy team is full of chimpanzees.
Looking at my smurfs in games, like this one when I played it a few months ago before parking it in Plat 3 (I used to park it in Gold just for the skin), a majority of the games I win aren't a team effort as much as I have to drag them kicking and screaming to victory.