I have a 4070Ti in the NR200P Max SFF gaming PC I just built for TV gaming and multiplayer with my son. On a flat monitor, running games normal humans play, it’s just fine. I can run MSFS (with the DLSS3 frame doubling turned on) at over 100 fps, and all other games I’ve tried on it max out the 4K TV’s 120Hz refresh rate just fine.
The only places where the 4090 in my primary gaming rig pays for itself are in MSFS at 5,120x1,440, and in VR flight sim titles. There, the extra memory does help.
But for normal games non-flight-sim-geeks play, the fact that demanding games are designed for consoles first means that 12GB should be plenty for a long time. The PS5 and Series X only have 16GB RAM total for both video and programs, so as long as games are targeting those as it’s gonna be the next console generation (2027?) before 12GB even starts to feel limited for normal games.