Stop release new characters twice a month…For the majority of players they wil be only a waste of slot in their rosters, for a very long time. 
For example, Mr. Fantastic was released last july (or august)…I will have his 13th cover today, at the end of Prodigal Sun event…9 months later. We don’t need new characters twice a month, we need ISO to level up the characters we already have…Don’t misunderstand me, I like new characters, but twice in a month is way too much to handle 
With multiple major movie events coming up, the pace may get faster than that..
Just remember, there is no requirement to have them all, unless you are a completionist.
So, DEVs are giving us characters but there is no requierement to have them all. Actually, they are useless (no sarcasm- 5* are the only ones you need) for players who dont buy ISO.
Finally someone honest here… and i always hoped maxing all heroes is the goal of this game… my bad 
While I agree with this in principle, (farewell, sweet Howard 
) adding more 4* characters does make it harder to focus on collecting the ones you already have as they become (relatively) more rare in tokens and vaults
PLEASE NO MORE CHARACTERS FOR 3 MONTHS!!!
I remember vaulting - was awful. my panther took forever. hulk did too, but can’t remember if that was due to vaulting. panther definitely was.
Yeah, there’s no chance of this game with an extensive roster of characters from a field that attracts collectors would ever have a significant percentage of completionists. 