Yep. The whole fake frames thing seems like a witch hunt to me. If you can actually get a 5090 and were previously fully utilising a 3090 or 4090, it is a significant upgrade, as long as it doesn't burn your house down.
And the generated frames are misleading because they don't work very well if your source framerate is low.
As you say you need a good framerate to start with before generated frames make sense so either you're already running well with a high tier card and are further able to show off the combination of framerate/resolution/detail level, or running a lower tier card at lower settings turning the graphics down further which can be a very obvious trade off. Less demanding games which are generally online competitive usually wouldn't do as well with any extra latency introduced, and the situation where I've heard it would be a good fit is emulators or any kind of game where the CPU is the limiting factor