Just ban large prs. They can always be split up, and usually as well as helping review it makes them less risky and easier to find bugs and roll back if there was a problem.
The discipline of splitting them up helps in almost every dimension.
So what do you think of Discord rewriting in rust, and AWS shipping an emulator that was ai generated? Do you think those were done with small prs? Do you think that it's bad they did those things?
Fully agree with a twist - ban dumb large PRs.
To add to my openspec shilling above, I've been known to "fix" large PRs by reverse engineering specs from them and building each spec out in a separate PR.
Last week me and a coworker turned a 15k line PR into 10 x 1.5k line ones that went in smoothly.