Azael is cool. He's Nightcrawler's dad. He's someone Mystique probably both loves and hates. He's the leader of an organization that's trapped in another dimension therefore M Day probbaly never affected his people. Also Azael could be actually be demonic becauce of a deal with demons and chaos magic. One strong force of chaos magic on Azael's side and the Scarlet Witch's powers wouldn't affect him at all. If the Neyaphem ever got loose, they could be the largest group of mutants on Earth. They wouldn't have been before M Day but afterward? Definitely. They could amazing, horrifying but amazing. A threat so large that the villians and heroes have to work together to deal with them!
All the bibical stuff makes some people nervous but that's easily retconed. You just say Azael is deluded. That he's thousands of years old but only becaues time works different in another dimension. In fact being stuck unaging in a hellish dimension for thousands of years while only centuries passed in the normal world could be what drove him and his people to insantity. Azael could have born in medievel or rennaissance times. That would explain the Bible obsession. In that time period mutants would have been seen as demons, angels, or witchbreed.
The neyaphem are probbaly more dangerous and certainly more savage than the Brotherhood of Evil Mutants. They're worse than Magneto's Acolytes They were born in a world where eye and tooth for a tooth was literal. They most likely wouldn't have a problem with crucifying or burning someone at a stake. They're bad guys as wicked and as barbaric as Apocalyspe, and though most wouldn't half be as strong, the sheer numbers would be a problem. Azael probably has a much larger number followers than the main universe Apocalyspe does. The exact numbers are unknown. There could well be over ten thousand of them! The numbers might be even larger than that. If the Neyaphem had been set loose in a version of the Age of Apocalype I think they would have taken over!
Then there's the Cheyarafim. They've got to be around somewhere in another dimension too. That doesn't mean they're good guys! Only that they oppose the Neyaphem. If the Neyaphem are chaos magic to the extreme then the Cheyarafim are a force of order magic in the opposite direction. If the Neyaphem get loose the Ceyarafim are bound to follow. Whoever Azael's greatest enemy in the Cheyarafim camp is, he's bound to be awesome and every bit as much trouble as Azael. That's if the writers handle it right. A major battle between those two groups with Archangel, the original Nightcrawler, and a returned from the dead Icarus caught in the middle is what should have happened in X Force: not a rehash of the Age of Apocalyspe and Dark Angel stuff. Waren shouldn't have been going all death, blue skin, and metal wings again.That's old news. Instead he should have under gone a mystical change to the bat wings ,chalk white skin, and red eyes, similar though not indentical in appearence to that of his counterpart, the Fallen, in the Mutant X reailty. His fallen like form could have been regarded as Neyaphem; this could have opened a whole bunch of new drama, especially if Waren could go back and forth between that and his more Cheyarafim like form and was regularly surrounded by both groups!
Apocalyspe is cool but not fresh, not new. No amount of reinventing is going to make him feel that way. A newer or less explored villian to rival Apocalypse is needed and Azael could easily be that villian.