is this all because of the lack of rim protection?
No, our rim protection actually isn't awful. I'd say generally the bigs are average at rim protection, it's far and away the best thing they do as a unit. Against Oklahoma State they were better than average.
We're 235th in the country in 2 point defense but we're 5th in the country in defending the 3. What does this mean? For us, we guard the 3 point line very hard, however we're very small and not appreciably athletic. The guards are good within the system but not great individual defenders outside of Miguel, who hasn't been as good as an on ball defender either this year, I think because of injures.
Long story short, we close out hard on shooters, don't give up a lot of open 3s but we give up a lot of dribble drive and our bigs aren't on the floor enough to make these tougher shots.
Against OSU Bryce Thompson went off, but they got lucky with that game winning shot. Avery Anderson hit it, Pack was all over him, and he was 1-6 on 3s before that shot went it.