I think that’s it. Messing with PTGS is probably enough. You’re looking for a pacing mechanism, no?
Introduce a new tolerance: Glancing. It starts where Superficial used to be. Glancing wounds have no effect; either two or three of them compound to a Superficial. Then arrange the others according to the original rules. This would mean someone with a MW of 10 & B4 Forte would have in the original system: B3 (Su) - B5 (Li) - B7/B8/B9/B10 (Mo) and in this: B3 (Gl) - B5 (Su) - B6 (Li) - B7/B8/B9/B10 (Mo). Someone who hits hard will still deck people, but usually you’re going to be working that much harder to get them onto the slippery slope.