Pair programming > PR reviews.
I've heard people scoff at the $$ cost of "mob programming". I think that view is totally myopic, for appropriate problems there's just no faster nor higher bandwidth way to transfer code knowledge in a group.
Plenty of people dislike pair programming, i don't dislike it but i do find it mentally intense, tiring. I really really enjoy that it's an accelerator for getting to done - not just i wrote the code but the code is correct - sooner.
Long way to say don't rely on pull requests when you could be doing pairing for the important stuff.
The only time I like pair programming is when I (or someone else) is stuck on an issue and we need to work together and bounce ideas off each other; otherwise I prefer to work on a problem myself rather than trying to be in constant contact with me paired person.