I think this is a good argument to underline "It's not _just_ the scale". Adding to this, the Github Code Review experience is kind-of broken, the way comments/threads are stacked in the PR overview has not improved, pagination isn't really a thing, and these issues are age old. Hopefully, one day, Github will mature.

The final step is challenging; likely the most difficult part is changing all the code references and imports. Shadowing changes would be straightforward. Training your likely 25-50 engineers to use the new code review UX would likely not take that long.

Considering the wasted engineering velocity during Github outages, it's worthwhile to do even a partial migration. Github's action runners have in my experience, been the most fragile part of the platform. Given the ease of moving build and merge queue runners to alternates, it's a no-brainer.