I haven’t read it in a long time but I remember the lore being pretty faithful to all three franchises & cleverly executed. If Jason is a Deadite & possessed by Pamela, that would still be man (Ash) vs nature (Pamela’s vengeful spirit), though it very much leans into Jason being used as a tool, which implies that the puppet master has agency beyond a mindless force of nature.
(Just having fun here and am happy for my hypothetical to be shot down.)
I would be interested in the Necronomicon’s chain of custody, since the first Evil Dead movie takes place in 1981!
The FXIII franchise always played fast & loose with how Jason keeps going, but I agree the Deadite angle really works in that regard. My argument for “what took Jason so long” is exactly the murder of his mother by a camp counsellor. He was R-ing I P at the bottom of Crystal Lake but came back for vengeance when she was killed. He even had her head enshrined in (I think?) the second film. Mama’s Boy.
That messes with the Pamela possession theory a little though. Interesting if he was agreeable to her setting up shop. Or maybe by the time one possessing soul is “killed” the other is powerful enough to come back. Like a tag team rampage.