How to properly frame/finish "trimless" interior doors?
If you look at the documentation for a commercial "trimless" door jamb kit you'll see that there's an integrated flange that creates a positive connection between the jamb and the wall. This mostly eliminates the kind of impact movement you've experienced. 



The flange also acts as a taping bead, avoiding the interaction of joint compound and wood, which usually isn't a good combination. 

You could probably retrofit a metal strip to serve the same purpose. Pre-formed steel found at a building supply store might work well to overlap and partially wrap the jamb. You could probably have a siding shop bend you some metal that perfectly fits your jambs. You'd then need to cut out for the hinge mortises.

Or, if your jambs are very securely fastened to the framing, and the framing is solid, try taping the joint properly with paper or fiberglass mesh. No joint should ever be finished with joint compound alone.