Higher-performing employees generally have more options than lower-performing ones, so they aren't desperate enough to go through a disruptive and expensive move in order to keep their job. For similar reasons, I'd expect senior-level employees to be over-represented, because they're more likely to have kids, a spouse, and an existing mortgage.

True but the switching costs are still quite high for higher performing employees and it seems like the pool of tech companies requiring working in an office presence is also gaining share (ie pool of companies to switch to without in office work is low).

Yes, as already predicted in numerous places we witness forming distinct styles of work with full WFH being in minority so the candidates who want to WFH need to be more competitive. If I wanted I could easily switch my job to an office-based one with a better pay; doing the some for a remote job is much more difficult (but well worth the effort!).

I imagine if tech companies continue to force the rto issue they will continue losing talent to other companies

Anecdotally I'm currently in the process of leaving a tech company and joining a legacy fortune 500, where I'll be full time WFH.