Big PRs sit for days. How do we fix that?
Make them smaller, because attention does not scale with size: a 50 line change gets real review, a 2000 line change gets a rubber stamp. Splitting by mechanical versus meaningful is the easiest cut, since the mechanical half needs eyes but not thought.
How do I review without turning it into style comments?
Automate style entirely, then the review can only be about substance. What remains worth saying: this breaks under concurrency, this loses an error, this name means something else in our codebase. If a comment could be a lint rule, make it one.
How do I know when it stops being worth it?
When you stop noticing it. If it has not surfaced a problem in six months, it is either solved or it was never the bottleneck you thought.