I think Banchero has all the physical tools to be a solid defender in the league. He's long/strong/mobile laterally, and has shown he can defend when he wants to. While the motor is an issue for some players, I don't see it being much of one for Paolo especially if he can get into Chauncey's system from the jump. Unless they're extremely bad, I don't see pre-draft comments about top 5 prospects lazing on defense being much of an issue-- I'm far more concerned about physical tools when projecting how these guys will be on defense. And Chet has tangible physical limitations to how effective he can be on that end (difficulty defending in space, lack of strength to battle down low, slow-footed, etc), while Paolo does not.
Also, Jayson Tatum wasn't really considered a strong defender at Duke either. Neither was RJ Barrett. Both are "plus" defenders in the NBA with some seasoning.
This is what the 
Ringer said about Tatum pre-draft:
- Lacks defensive mentality. Loses focus off-ball, dies on screens. He has the ability but doesn’t play with much effort or NBA-level physicality
 
- Lacks defensive versatility. Flat-footed on the perimeter; gets toasted by guards. Thin in the waist, so gets overpowered by bigs
 
While they said he was a competitive defender at lower levels, 
they also said this about Barrett:
- He’s a ball watcher off-ball who routinely misses defensive rotations; on-ball, he often falls out of his stance possibly due to a lack of interest, awareness, or energy.
 
Here's what 
they say about Paolo:
- A strong and quick defender who could potentially develop into a versatile on-ball stopper. He can slide laterally against smaller guys and might be best suited as a small-ball 5 due to his comfort switching screens.
 
- Effective help defender who can alter shots around the rim using his length and athleticism—when he’s trying.
 
- Defensive effort fluctuated in high school and has absolutely evaporated in college. Every game, he has instances when he doesn't even bother to contest a shot or rotate to help. He’ll sometimes lose track of his man and he could be better about boxing out more frequently. Banchero shoulders a lot of responsibility on offense, so he might be conserving energy.