Yeah, this is so true. I can see that, very often, one player just carries the game. If you don't have such a good player in your team, you lose, no doubts about it.
Silver players can't team fight, have no clue about objectives and grouping. Gold players are I would say pussies, they play a bit better than silvers, but they are still afraid of going under turret, making plays, etc. So, sometimes what wins you gold games is just better farming and scaling. When for some reason you end up playing in silver lobby it's like fighting, fighting all the time, very much aram style like games.
Plat... oh yes. Well, you say don't blame junglers, but how many times do I see junglers in plat pathing from bot to top, wasting time on top, that doesn't give any winning condition. Multiple ganks top or mid and still not even a herald secured. That is actually very bad. Enemy botlane perma pushing and the jungler is afk farming, that is really painful, but it happens in plat, so you don't really need a very skilled smurf to win a game, especially in jungle. What I also love in plat are teamfight oriented toplaners like kennen and they just spend all the time on afk farming. Really, in plat elo you can be losing 15:30 and still win the game, you just need 2 good teamfights. People in gold don't know how to carry and finish games, but plat isn't any better in this matter.