I agree it made sense from the perspective of the characters motivations at the time.
But that said, if you're going to tell a story where an uber bad guy is going to kill off like 80% of your male supporting cast, IMO you should probably have used the lion god instead. There's just more pay off to that. YOu have this character from another franchise you drastically alters your characters status quo, but is basically never seen or heard from ever again.
And with later retcons to Morlun being more Spider-Man specific, it's less likely NOW that he'll show up again than at the time.
I loved the idea of Morlun being used in general... but I don't think having the lion cult summon him made sense. And I probably wouldn't have had the character play such a big role given he was basically never going to be used again.
But hindsight is always 20/20. Overall I did love that story arc... I think it's one of the most underrated BP stories.