Generally characters with healing/regen or defensive abilities will have lower health for balance.
But then came BRB, dropping Protect tiles all over the place and rocking 65k health (at 450), and now we have his buddy Apocalypse, who also loves shield tiles and has 84k health at 450. What gives? Is there some dimension of the game where this isn’t a problem?
Make sure the new characters seem required to compete so people keep whaling/chasing them.
One easy way to do that in a game with 210 or so characters - and many, many move sets which have a hard time distinguishing themselves - is boosting stats.
I also think it’s worth pointing out that characters who generate protect tiles or have mechanics that reduce damage intake tend to have normal or higher health relative to their cohort so neither Beta Ray Bill nor Apocalypse are exceptional in that regard. For example in the 4* tier you have Luke Cage, Juggernaut, Rogue, Sandman and The Thing.
Among self-healers, Okoye is the notable exception. At the time of her release, she had one of the highest health pools and still falls on the higher end of the spectrum in comparison to her 5* peers.
The problem is that BRB and Apoc also do A LOT of damage. In other Tiers (like the ones you mentioned) usually don’t excel at both defense and doing damage.
See my comment above. In most games with a wide roster of characters or even with customizable archetypes, there are tank builds who focus a little too much on defense while others have mechanics to dish out damage as well. MPQ has no aggro mechanic, so tanks have high health, usually some defensive merit and some add a pretty devastating move. Side note, I think Apoc is the first tank in this game with heals. Is he MPQs paladin?
Juggs is a premier damage dealer through enabling
Luke Cage has a dandy nuke
Rogue is a moderate damage dealer
Sandman is a moderate damage dealer
Thing is low damage