Realistically the Celtics package would be Jaylen Brown + Kings pick + Future Celtics pick + Smart and/or Morris. They CAN swap Brown for Tatum if absolutely necessary but chances are they won't need to because no one else will have a better package than that to offer.
That team would definitely be better than the Sixers. Kyrie would average 30, Kawhi cancels out LeBron, Simmons has already been shut down by Stevens defensive scheme and will again, Embiid will get off but Horford would have his 20 to offset that, Tatum would have free reign to dominate whoever is matched up on him, and Boston would have the better bench