The balance in this game has been screwed for a very long time now because Lilith realised that they can't make money while keeping the game balanced.
If they release a premium hero that does less damage than the previous premium hero no one will buy it, people will rage and demand refunds, forcing them to redesign/buff said hero. (this has happened multiple times before)
Look at a game like Dota2 or Heroes Of The Storm (both on pc) where the meta is evolving almost every day and skill matters more than $, these are the golden standards of how balance should be kept, there heroes like Ember or Esabel could never exist alongside Wonder Woman or Ursula that deal thousands of percent more damage.
At this point with something like 250 heroes in their roster its impossible to go back and rework every single unused hero, which won't bring them any revenue anyway, so they just keep releasing imba heroes every month, catering to those than don't care to spend a few hundred bucks to have the best team in the arena at any given point. this is the nature of business.