Islanders need a center more than anything. Barzal is not a center, and Nelson is a borderline one himself.
If you could put those two on one line, and add a Horvat to the group, it looks a lot better. Problem is, they probably can't make that happen.
Pageau for 5 mill is nowhere near as bad as Palmieri or Bailey for 5 mill though. Pageau's contract is actually pretty good for what he brings. Top notch PKer, excellent in the dot, makes his linemates better, and can put up 45-50 points in a shutdown 3C role. He does get PP time too but he is not much of a factor there. He is effectively Kerfoot if Kerfoot was good enough at FO's to play center full time, and people will be surprised to see what Kerfoot gets in UFA...