They most definitely are counting on his spacing.
Sengun has no range whatsoever. Can't have another non-shoter in the starting lineup.
Amen comes off the bench and doesn't play that many minutes with Sengun.
Amen and Castle just can't share the floor.
Much like Castle and Sochan. That would be my biggest question mark with Castle.
But we're still far away and in BPA phase, even if it's not a good fit. But no way two of them would start together.
Obviously, Brooks is just a solid role player. But shooting is the most important skill on offense for perimeter players and you can't just replace a high volume shooter with a player who doesn't shoot.
Imo, Rockets either trade the pick or get Risacher/Sheppard. I can't see them taking Castle.