Are you asking my opinion on who will be better at rebounding and defense?
I was commenting on your post where you said we shouldn't expect inefficient shooting from Ihnen and that he'll be a better passer. He will not bring those things, I'm glad you've seen the light and we can dismiss that silly argument.
IF we are now pivoting to my opinion on how Ihnen will be at defense and rebounding, that's fine.
Assuming he is healthy, I think Ihnen would be an OK player on defense if he's playing SF. I think he'd actually be a pretty good defensive player if he's playing the post. Rebounding, he will be a good rebounder.
If Ihnen is playing the 4/5 next season, I think he'll be a decent player. I've been told there are just no minutes at the 4 because we have Garcia, but if Ben can somehow find a way to play him at the 4, I think he could be effective there.
If he's playing the 3, I think he'll struggle. He might be OK on defense but it will absolutely gum up our entire offense by having a wing who cannot dribble, cannot shoot, and has shown absolutely zero guard skills (I thought the same thing with Battle and Battle has at least the mirage of some guard skills).