Not all merges are equal, even if it's a monorepo, it's probably rare that you'd have to look at the whole codebase to implement a new feature or find the root cause of a bug. Once you start looking at the history of a specific folder, it becomes more tractable.

Of course that does require some folder structure, and agents are not necessarily great at that, but they're still decent enough that you do end up with many folders not being impacted hour or even daily.

I am not sure that I can agree with this at this scale, especially for the hotspots in the code. But I admit that I am speculating here.