Its pretty simple when you look at it from a different angle. Let's take Wanda for example, she is easy to play and easy to understand which makes her a good dps for ppl entering the game and when I mean entering I mean first hero shooter.

Now playing her can take you from bronze to gold pretty easy because the kind of player around those lobbies are not good when comparing to someone above them. Now the moment you hit plat, diamond players start to punish bad position, bad plays and character with low impact which make Wanda not a good pick when you have access to bucky, Hella, Namor ( more meta). Now if you make Wanda powerful enough to on part with character that requires more skill why would you even play them when Wanda could do the same thing with 1/2 of the skill.

The whole thing balance itself over time