Dalembert is still the best conventional defensive center we've got.
With opposing PGs turning the corner on Jose, you need a presence in the paint.
With Melo probably being just OK, you'll need a big with their hands high up in the air to assist.
Jason Smith on O is going to operate from the outside in, not inside out. On defense, Jason is going to be scrappy and get some deflections, but I don't yet think he provides the paint presence Sam does.
Sam is good. Is he the best? No, but many teams still don't have a player like Dalembert in the middle.
He makes the first unit make sense. Add in Acy and you have defensive intensity and grit to go with Shump and the 1st Unit can come together as a team defense and handle themselves.
We'll get penetrated on more than we like, but unless every penetrator has a world class floater, we can still defend the rim.
Remove Acy and put in Stat like some want and then you have problems in expecting Sam to account for the whole frontcourt. You put in Acy or try Smith for a twin tower effect which may also work for stretches.