Yes - I would trade Smart for Noel any day, any time, without a moment's hesitation.
To me the concept is simple.
Noel is a big who offers length, athleticism, rebounding, rim protection and defensive versatility in the front court - five things we are in dire need of.
Smart is a guard who offers defensive versatility on the perimeter, where we already have Avery Bradley, Terry Rozier, Jae Crowder and Jaylen Brown on guaranteed contracts.
What Smart offers is nice to have, but for the Celtics he is largely redundant.
It would be FAR more productive to trade that redundant piece out in return for somebody who fills a very real need.
We could argue back and forth all day long about which player is better, and which has more upside, and all the rest. There is no clear right or wrong answer to that - only opinions - since each players offers different things.
Nobody can even TRY to argue about which player fills more of a void on this team - it's blatantly obvious that we need Noel's talents far more then we need Smart's.
Problem is that if I'm Philly, I don't think I'd do the trade. They have a team full of bigs and desperately need a PG, but if I were Philly I'd want a more pure PG (like Dunn) who is a natural playmaker and ball handler who can create plays for their big boys. I'm not sure I'd have a lot of interest in a tweener like Smart is capable of handling/distibuting the ball, but it's not really a strength of his.
Also, I'm not sure if you can seriously start Smart alongside Simmons and Okafor or even Simmons and Embiid. There is zero floor spacing there.