I’ve posted in other comments that a lot of the initial studies were based on self reporting surveys, not actual measurements of productivity. One study that used actual measurements from a call center later revised their report as there were issues found like increased call backs.

And as for in-person versus virtual, I’ve seen a lot of staff don’t ask as many questions online as they do in person, even with video conferencing and chat being widely available. You also have some cases where senior staff used to do mentoring and providing some technical direction on projects they aren’t working on no longer doing so either because full remote tends to push everything up to the lead, which ends up getting drowned in more communication than hybrid. Sure, the senior staff may be more productive by some metrics, but the department isn’t and senior management is going to to try to fix issues on the department level. And as others have noted, there is a shortage of qualified staff, so you can’t have everyone be senior staff.