I think Noel, right now, is probably a more impactful defensive player than any the Celts have.
I would not be surprised if the same is true of Embiid once he starts playing.
I think Okafor, as soon as he starts playing, will be a more dangerous offensive player than any the Celts have right now, with the exception perhaps of Isaiah Thomas.
The parts in bold are the key factors here.
I agree with you that Embiid has more defensive impact than anybody on our roster. But he is such an offensive liability that it's questionable whether he actually hurts the team more offensively than he helps them defensively. There are some statistics out there that would suggest that this is, indeed, the case.
I'd also argue that Thomas has just as much positive impact on offense as Noel does on defence. On pure offensive statistics (basic and advanced) you could make a legit argument that Thomas is one of the top 5-10 offensive players in the entire NBA. You could probably make the same argument for Noel on defence. Thomas hurts his team just as much on defence as Noel does on offense. Pretty hard to argue that Noel gas more overall impact on his team than Thomas does for Boston.
Bradley isn't as dominate defensively as Noel, but he's a two-way player who contributes a significant amount on both offense and on defence. He's our second best defensive player after Smart, and he's also our #1 scorer. Again, hard to argue Noel is better than him as an overall player.
Sully has defensive limitations, but does he hurt Boston as much defensively as Noel does offensively? Again that's a pretty tough call - especially given Sully is a significantly better rebounder than Noel.
The fact that we have three impact players on our roster and Philly only has one instantly tells you which team has a better talent right now. Especially considering none of those Celtics players are older than 25 (so some potential is still there for all three of them too).
Would you trade Bradley, Sully and Thomas for Noel? I bet you wouldn't. I definitely wouldn't. Neither would Ainge.
The second important part is that your comments about Embiid and Okafor are clearly all speculative. "I wouldn't be surprised" and "I think". Why? Because there is no possible way to know right now, hence the risk. No matter how confident you may be in the ability of those guys, nothing is sure until they step on the court.