Pageau is the type of player a coach needs to win playoff rounds for his overall body of work.
Pageau is the type of player his teammates love as he backs it up while having their backs.
He is also in his prime and needs to play for a team trying to win now. So Ottawa got solid draft capital while NYI got a much needed defensive centre who can play up and down the line up. While he doesn't have a top-6 C level playmaking skills, as an elite 3rd line C he is more effective in the playoffs than some of the typical 2nd line centres.
Clutch.
In retrospect I hold the same view as I held when the trade was made - WIN-WIN for both teams.