Battery life would be the big thing, I think. There's not a single person I know who wouldn't like having Linux on their M1/M2 Macbooks--they're beautiful devices--but if you're not getting something approaching MacOS's battery life, then there's not that much separating it from another similarly-specced ultrabook.
I doubt there would ever be parity but it could be good enough. Have to hand it Apple OS team, they know how to squeeze a lot out of there hardware. A while back I was trying to get an old G5 running and looking at the various OS options, many said just go with MacOS 10.4 - it was the most optimized OS for the system even today. When software and hardware work together, it can be pretty cool.
I mean, for a kind of museum piece, to get the true experience of using the computer I’d agree for sure just use original OS. But if one wanted to be able to use it for most functional purposes, it’s sad how the complete lack of backcompat in MacOS makes using an old MacOS tough — which is sad because new Linux often can work surprisingly fine on the same hardware. Like, current Debian on a 2008 Core 2 Duo is a fine computer that you can browse the Web and do basic office tasks on. It was shocking to me!