If Noel was a 2nd year player keeping him over Jah would be a no brainer.
But Jah has two more low cost seasons where he can improve (he's unlikely to be close to a finished product right now, and I think the knee has slowed him down this season).
Whereas Noel wants to start, wants starter's money, will be a RFA next year, and is unlikely to be happy playing second fiddle to Embiid over the long-run.
With Saric and Simmons, and maybe Ersan resigned for a couple years, the Sixers have plenty of better options at PF than Noel. Heck, RoCo can play PF credibly.
So it's hard to justify going with an Embiid/Noel experiment and limiting Saric's minutes when Simmons returns.
And Holmes deserves some PT.
As far as defense, the improvement came more from cutting Hollis and bringing Sergio off the bench, I'd like to see some more of TLC for that reason as well.
When the perimeter players do a better job on defense, Embiid doesn't have to get out of position as much (learning curve here, both Embiid and Noel are over aggressive going for blocks, but Embiid has an excuse, sometimes I think Noel is "stat padding" for a new contract). In fact, if they played better perimeter defense (and Simmons will help), Jah's limitations won't be exposed as much, and he's actually better defensively against opposing centers than Noel (doesn't get pushed around in the paint and is a good shot blocker with his reach without leaving his feet) - Jah's problem is lack of quickness helping out. So the less help he has to give, the better.