Assuming you have a well-working team, real-time still seems more efficient to me, at least at my current job.
- Real-time communication in person (face-to-face)
- Real-time communication remotely
- Asynchronous communication remotely
The scenario you mention "gets asked something but doesn't reply until at least two others pester him via phone repeatedly” seems to be in the category "Real-time communication remotely" (phone is real time, but remote). I think that area is problematic too, as my post points out.
Overall, I guess my experience has been that asynchronous communication remotely and real-time communication in person are both better than real-time communication remotely (aka "endless Zoom calls"). Real-time in person seems to have more feedback loops where someone who is badly behaved faces social consequences (e.g. not invited to lunch, etc.); and asynchronous remote seems to prevent it a little by giving everyone an equal amount of space to express their thoughts.
But overall, yep, I think all of these are assuming less-than-ideal coworkers. But...that's reality, isn't it? With perfectly behaved coworkers, all three options can work perfectly.