Although it's one of the "different" things, along with memory model, the page size is the same for Fedora aarch64 if I remember the discussion right.
Is POWER9 compilation generally poor compared with other targets? It didn't seem so to me, apart from a pathological case on one benchmark set which IBM addressed swiftly. They've been supporting GCC for rather a long time.
That used to be the case until https://www.spinics.net/linux/fedora/fedora-kernel/msg12805.... which put aarch64 to 4K. I argue there should be a workstation ppc64le spin that does this, but I understand why Fedora doesn't want to put the releng resources towards a niche audience.
I agree IBM's autovector stuff is quite good in gcc but there's no substitute for hand-rolled assembly sometimes.
Is POWER9 compilation generally poor compared with other targets? It didn't seem so to me, apart from a pathological case on one benchmark set which IBM addressed swiftly. They've been supporting GCC for rather a long time.