Your defensive performance doesn't look too out of whack to me. Pretty good overall, strong against 3s, pretty good TOs for MTM. FG% is a touch high, apparently from some interior D weakness (low ATH & walk-on at C help explain that). Your last couple of recruiting classes focused on ATH and SPD more, which will improve your D in the future.
IMO switching to HCP/Zone will make your D worse, at least short-term. I don't like combo Ds personally, especially D3, but I believe others have had success with them. Plus, your roster is probably set up best for MTM. If you want to switch to try something different, de-emphasize DEF rating in recruiting and increase the importance of ATH/SPD. Don't ignore ST, although it won't be as important for you as I'm used to making it (my Press teams are generally FB/FCP).
Personally, I would start Little at C and Knickerbocker at PF next season, probably regardless of what defense you play. I don'tlike having 2 guys the same position and class, so I would try to get a juco or transfer for one of my C recruits. Or you could reshirt one and play a PF there a lot.