A bigger one is what does it say about the product? People are already using low settings disingenuously to say X game is ugly and not up to par, a potato setting would just exacerbate this and from an art standpoint do the developer really want to stand behind such a gimped product?
To clarify, I'm not saying that games should design for the lowest level of hardware, but they should make it easier for people with lower tier hardware to adjust the game to run better. Some people might use it disingenuously, but I really think people will see right through that if the potato setting became common enough.
You made another point about lower details not being enough. In cases where it isn't possible to improve performance without sacrificing gameplay, I think developers should put gameplay before making the game playable with older hardware. Its not about demanding all games be playable on a mid-range machine from 2010, its about asking developers to make an honest effort where possible.
As for FSR, I don't think its a full solution since it still uses the same model and texture quality as the lowest setting (if not higher), which could mean higher VRAM use than needed. I'd rather see FSR paired with downscaled textures and simplified models.
I've been playing the RTX mod for Half-Life 1 recently. If its fun to see old games with new techniques on them, what about new games made to look old? I'd love to see someone make a tool that does the opposite of RTX remix - downscale all the textures and simplify the models, remove a ton of shaders and such. Probably never gonna happen, but it's a cool idea.