I don't think I ever put any of my laptops into iGPU-only mode, it's stupidly low-performance with little upside.

Not sure if this was in jest or not but I can say the same. Both when I daily drove a MacBook Pro, and when I was using a Razer laptop as a desktop replacement at the height of the GPU shortage (it DID NOT like charging the battery all the time, eventually it puffed up and I had to remove and recycle it, oops). Though I do see the utility of auto-switching for the average user, so I definitely won't complain about the existence of it. :)

I have. By specifically choosing an iGPU-only model so I wouldn't have to deal with all this multi-GPU nonsense. And AMD iGPUs are more than fast enough for light gaming which is the most I care to do on a laptop - just make sure it's a recent iGPU design in the GPU you get.