My vast experiences ranging all between bronze and gold says differently. Hell, even the vast majority of the forum trolls on here will agree, "If you can't carry your team you deserve your elo trolololol" Don't pretend like the scrubs between bronze and gold know wtf they're doing in team fights..
7/10 games you'll get 2 of the 5 who simply won't give a shit to listen.
7/10 games you'll get feeders/trolls/afkers or all of them at the same time, depending. Essentially making it a 4v5 or worse.
910 games you'll get those players who don't know or can't focus the CC'd target, or know how to prioritize in team fights essentially making a winnable teamfight impossible.
Yes team fights win games... but the chances you get 4 other players in bronze through gold who know how to do it and are willing to work as a team and not pretend like they're god and everyone else sucks is slim...
FYI. I never said Team fights don't win games.. I meant. Being a good player, and great team oriented player does nothing for you in low elo.