I have 7800x3D + RTX3080 and frequently run games at native 4k 60fps with mostly medium to high settings, or 1080p 120fps-240fps ultra, I can't get this game to run at 60fps consistently at 1080p even when I put it on the lowest setting and put DLSS to preformance mode. If this system is struggling even with DLSS at 1080p to hold 60fps, I can not imagine how bad it is for the vast majority of machines out there. What really bothers me is it seems 100% intentional as the steam hardwear requirements tell you you need frame generation to even expect 60fps.
Sounds like a cpu issue (not yours, theirs) if it can't even run 69 fos while upscaling to 1080p. Big yikes. MH usually ran pretty well on PC.
I know the cloud option ruined perf in MHW, could see if lowering thst helps at all or playing on medium and see if cpu perf goes up, then trying settings a few at a time to full and see which breaks.