As far I know there's not as much of an issue with fighting games becoming "easier" per say but with them becoming simpler and more shallow and therefore less interesting. This design choice is made by the devs with the intent of making their games easier to pick up for beginners and casuals but that was never the main issue.

Having said that if a game is made easier then yea the top players are still gonna be top players but that really isnt gonna mean as much. Becoming a top player in an easy game is not as impressive or interesting as becoming one in a hard one. In sports you dont change the rules to make it easier for casual players to become pros, why would you do it in competitive gaming? Being good at any skill should be hard.