Nobody knows for sure what Heimdall will look like once they release him.
Although both Alby and M. N. both have revive, they work very differently. Might be true that overall she is the more useful than him,I cannot judge that. Even if that is true, most people would be super-happy to get either of them. If there were a TC20 reviver out there, who would make Alberich mostly irrelevant, I could understand a need for a buff. As it is now, he has an almost unique special effect and everyone who was lucky enough to get him should be glad.
As for Ares: He might be less useful in tank position nowadays but he’s still an awesome hero in titan fights, I suppose. Also I can imagine that he’s pretty strong in raid attacks.
Athena is still the best 5* defense debuffer in the whole game.
Musashi isn’t great compared to several newer yellow 5*,however he at least has a pretty high attack stat and should be quite good in raid attacks.
As for Thoth I agree. Thoth deserves a buff and there already threads requesting this.