I'd say about 80% of games any given player could make decisions that are incredibly better, whether that wins the game is debatable but the sooner you make a mistake the sooner you've potentially thrown the game. (e.g. you dont shoot an enemy with 20 health so you can get more damage shooting a full health tank, he escapes and kills 5 tanks)
that is very untrue, no matter what tank or what team you have a chance to win the game, and every mistake a player makes compounds, such as my example above. If it's the teams that dictate winning you must ask yourself why some people have 40% wr and why some have 70%, obviously they get the same teams because every team is terrible (on average), so it must be player related yes?Honestly though, blaming the teams, is the most sensible thing to do, given the nature of this game, if a team loses, it loses not because of one single player.