The example with the Ork horde is unsatisfactory in your opinion?
I would remedy it first through fluff and only later resort to crunch. For example:
- have the Orks come up with some form of tactics. Even Orks are not that stupid to keep running to certain death if they see all their fellows cut down. Ofcourse their grasp of tactics is rudimentary, but they might throw some Grots to the PCs to tie them up or even their way with lots of thrown grenades.
- where did all the bodies go? sooner or later the tomb and hall would be filled with dead Orks, granting the new Orks some form of cover and limiting PC mobility.