To be honest he seems to want to do too much at once, and consequently isn't truly good at anything.
Dead for innumerable ages is great in theory, effectivly he's going to be immortal most of the time if you play decently and don't make him fight say a bloodthirster. But the low minimum wounds required means you still can't risk it and play like that cuz he will occasionally die to very minor threats, like a handfull of clannrats.... Putting him in a weird situation where he is increadibly sturdy, and should be willing to take risks. But can't because he will occasionally die to some stupid minor threat...
Azerite barrier does a stupid amount of attacks in the right circumstances, but can also be completly harmless if your opponent pays any sort of attention and sends the right enemies to kill him. Which means he's in this awkward situation where he is both good and utterly terrible in combat.
Magic-wise he has great casting bonusses. But celestial deliverance doesn't really have the needed range without balewind, forcing him to go closer than he wants, and the slann lore is just underwhelming. Plus the difference with a regular slann isn't that great. So really, unless you really want celestial deliverance you might as well just take a regular slann.
And lastly you got some random support abilities stapled on with the free CP & his command ability. Which again, aren't bad, but feel a bit out of place when the rest of his special rules focus on dealing loads of damage and on being immortal. And again, his support abilities aren't major enough to label him a support hero.
Honestly, fixing this wouldn't even be difficult. He wouldn't need to be in the 600-800 prize range by any stretch. But he needs to actually focus on a role and stick to that instead of half-assing all of it. Is he going to be a close-range combat-ish hero with powerfull defenses, attacks and powerfull short range spells? Is he a backline squishy caster with powerfull long range spells? Is he supposed to be sturdy and willing to take risks? Is he a glass cannon that can die to a few clanrats and thus avoids any and all risks? Is he supposed to be a powerfull support hero? Right now he tries to do it all, but isn't amazing at any of it.