Should you actually have a main if you want to rank up?

I like to play a different character every match, I play mostly damage these days. I think on support its easier to have a main because most of them can fit with any game. I feel like for damage its better to play certain things based on the map or what the enemy is doing. I like to play tracer, reaper, cassidy, ashe, bastion because I find these characters easier to play. I am only platinum 4 but I feel like when I play my best heroes I win too easily.

I stopped playing the hard characters like Mei, Torbe, hanzo because I always miss their shots no matter what.