I think it's pretty common for CI, but I guess that use case can handle a little lower performance.

And for each CI compile, how many times have devs done an incremental compile? Probably a lot.

Well with a good build cache, CI can do things like incremental compiles too. You can even put the cache on the network and have most of your CI use incremental compiles.

I've worked on projects that took over an hour to compile. I would not like lower performance for CI. Many workflows require successful CI runs before one can merge for example.

It's really only Rust and C++ that ever take that long, right? IMO, that's simply the compiler being unacceptably slow. I also can't see a slightly less efficient parse tree being a big factor in compile times this kind of length...