The mechanism is irrelevant. A 90% drop in performance is the problem, requiring a $5,000 GPU to render 60 fps at 1080p.
Repeat: lol, no.
I have tried it on my 4080 super using the patched dlls for 40 series, at 4K the hit is indeed massive.
Assassins Creed Black Flag Resynch:
4K Res Ultra settings with 2x FG tops my FPS at 118 fps (playing on an LG C4 OLED at 120 hz) with 280 Watts comsumption (of a max TDP of 320)
If I activate DLSS5 with those same settings performance literaly halves so im around 55-60 fps with 2x frame gen (which is not good) @ 310 Watts
I lower the resolution to 3200x1800, my performance goes up to 80 FPS with 2X frame gen, playable but still a tad low.
I lower the DLSS model resolution to 50% in optiscaler setting and perfomance goes back to around 100 fps.
Played 3 hours like this and I must say I was pleasantly surprised, for this game that tries to look photorealistic, the results are outstanding, I simply toned down the strenght to 75% as it was a bit too harsh but left everything else untouched and it looked amazing and very photorealistic, not onlty the characters but the enviroments too.
Jungle vegetation suddenly had much more self shadowing, the colors looked more realistic it toned down a bit saturation but also added like soft reflections on leaves that had direct sunlight, also seemed to add subsurface scattering to the vegetation as well, it was simply amazing.
So if you tweak it correctly you can get great results with playable frame rate and ON PREVIOUS gen cards! (thank god for modders)