Learn new heroes…pretty sure the game was not made with the intention of “maining” anything…you’re supposed to have a varied hero pool…most of the top players play several heroes.
It’s part of what “being good at overwatch” entails
And they do…that doesn’t meant they won’t be the inferior choice relative to other heroes though…some heroes simply work better than others given what the game calls for…At higher levels certain characteristics are more beneficial and make for better choices…
it doesn’t even have to be planned either…Expecting all the heroes to provide equal value is pretty unrealistic for a game like this