This isn't a matter of opinion, this is a matter of: 

Everyone understands the absurdity of superhuman abilities, even with numbers or lack of numbers behind them. And saying that guns are superior to Captain America x 5 characters because they have the potential to instantly kill them ruins the fun of it. Guns aren't high tier because nobody wants a fight to end instantly with a single gunshot.

It wasn't a problem before, because it was fun before.