@Tom McAndrew posted a great Roob write-up summing my thoughts. After last season, the offense needed to be redesigned from the ground up.
If you bring in Mannion, then you need to push your chips to the middle and give him complete control to implement a new system.
There was always likely to be collateral damage. Frankly, Stout surviving 3 coaching regimes was a complete anomaly. We were lucky to have him for as long as we did, but change is inevitable and now is as good a time as any.
And I say this knowing that Mannion’s success isn’t guaranteed. But the Eagles haven’t been afraid to blow it up and redesign. That’s led to multiple titles under this owner and GM. They have to take their shot.