The most friendly option to developers would be not building the perf
build by default but this has been repeatedly shot down in the past.

I agree. But I also find it reasonable to make it so one won't accidentally build a dev build when trying to make a release. (that being said, in the Ocaml world, things have been going the other way, where, if I understand correctly, `dune build` builds development version, while `dune build @install` builds release artifact). I can't say I have a strong opinion on this.

1. -c doesn't work very well compared to ./configure for me and picks
up the wrong versions of alex/happy as installed by hadrian rather
than the ones provisioned by ghc.nix/. I have tried to avoid it anyway
after encountering some problems.

If anybody else have such issues with `-c`, please share your experience in the thread. I haven't had any problem so far, myself.