I highly doubt you'd be able to do this outside of a small company, or a small self-contained team.
I've seen those exact questions in PR templates before, but they almost always end up ignored or answered in the most obvious surface level manner. I see no reason you'd be able to reliably get reviewers to do any better. Really understanding a PR takes time, and the time to do that is one of the first things that gets jettisoned when anyone is under any kind of pressure to deliver.
>But sometimes a redesign can be super compelling to everyone, and the question is: do we want to be stuck with the subpar version?
If it's really going to make a difference sure. The point is is this the case frequently enough for the process to have a positive ROI. I don't think it is.
>are not really about quality
If they aren't improving quality, then they better be improving velocity. I highly doubt this is the case. I've never personally seen it. Given the enormous cost, I want hard evidence to justify that cost.
>when everyone architects their own way,
That's not the alternative, before mandatory PR reviews, we still had, design reviews, white board sessions, code reviews, pairing sessions, planning meetings etc...
>This is however a big departure from your original statement that PRs are the absolute worst time to review the code.
Catching a problem just before merge after someone has written everything they plan to merge is self-evidently the worst time to catch a problem (next to after it has been merged of course). Now you can argue that it may be the most likely time to catch a problem, but there's no arguing that it wouldn't have been better if the problem had been caught earlier.
My argument is that in addition to be the worst time to catch the problem, it's not actually catching real problems enough to be useful.