Well for one CJ is a proven 20+ PPG scorer. That is something they really need. They need a player who can ISO and get you a bucket, CJ would be a perennial all-star in the east too.
I wouldnt do that deal if I were Phila GM/owner, no way whatsoever... they are in the rebouilding process and I say roll the dice for the couple of years and see how team develops, in that time, Saric value will become higher than it is right now cause he is sure thing and when it comes to Fultz, well he practically didnt play this season, so its hard to tell if hes gonna develop as they expect etc
they gain absolutely nothing by adding CJ while sending Fultz & Saric away... they should trust the process for couple of years and see how it goes, if it doesnt work, then do some trades, shake things a bit... Embiid and Simmons are clearly untouchable on that team, both now and in the future, but when it comes to Fultz, Saric, Covington, they all are valuable assets and I believe they will be available in the future if things doesnt work as expected, or just to get better player(s) by moving them
and I dont know Phila cap situation, can they afford big contracts as of now, but you can see their roster is filled with talent and veterans, so CJ doesnt make sense for them, other than being a bad deal..