I didn't downvote but it's because parents comment are anecdotal and not providing further data one might be able to engage/confirm/refute ... and therefore I learned nothing from reading it.

I'm also running a dual setup of i3/sway and the only reason why I still keep i3 around is screen-sharing in jitsi and similar. and my experience is that wayland has a lower use of CPU/memory than when running X (i3) but it's not why I prefer sway. (I'm using sway with "xwayland disable" so maybe this is where a lot of resources are saved). But the whole discussion is pointless without verifiable benchmarks.

Another example I like is the Nokia N900, which ran X on a phone no less, phone hardware from 2009, and it was pretty good there.

Part of the problem is surely software bloat over time on higher parts of the stack, rather than X itself. You couldn't get the 486 in the comment above to run recent gnome or a recent browser. But you could run software of the era well.