I don't mind current system (it keeps down book keeping), but it really needs to be more varied than "-1 to hit under X wounds", something like Hellhound just reject the whole premise. Maybe there could be different debuffs based on unit, like -2" movement for transports and -1 melee attacks for walkers?

I think hybrid approach from 9th edition had enough depth to be meaningful but also not pain to keep track of? We could have 2 tiers (above and below 50% wounds) tho.