m8, I got placed Silver 5 in provisionals. I main support. In about 60% of my games, I've done well, going for example 1/5/15 on Nami - and losing. Despite playing my position to the best of my ability, I've got an abysmal 24% winrate and am now Bronze 4.
When it's 30-6 and I'm getting trolled with 'No' votes by teammates who couldn't outplay a wet paper bag, I don't AFK, but don't expect me to go into the 10th midlane team fight and help them feed the other team even more, either.
EDIT: For clarity, in that time, I will be away from the bs, farming as best I can, recalling to defend when there's no choice but to do that, and initiating another surrender vote as soon as I'm able. If somehow, by some miracle, the count starts to even up and my team actually manages to take a turret or two, then I'll start helping again - so far, this has happened plenty of times in Blind games, but not one single time in Ranked have I been on a team that mounted a comeback OR played against a team that mounted a comeback. These things don't happen in Bronze.