I basically agree with everyone, but with a couple additional remarks:
I really find the fonts choice odd: we really mean to have monospaced fonts *at least* in the editor. If somehow Haiku doesn't provide a sensible default for *monospace*, sure, use a specific one that makes sense there, but please keep it monospaced.
Otherwise, I think it depends on how *required* those settings are for the relevant options to work on Haiku or not. If for example Haiku ships with its own browser and using *firefox* will either virtually never work or feel out of place, sure. If it's a preference, not so much. So at a glance, I'd think that the default apps change make sense, but the fonts not so much.
@elextr's and @eht16's point of distros patching their favorite defaults make sense, but I see one main difference: we've got a preprocessor define to work with here, like we do for Windows and macos, whereas there's nothing similar for Debian/Fedora/Gentoo/Whatnot. This makes integrating those changes realistic (they only affect Haiku), whereas the ones from Linux distros's preferences would be a lot harder to integrate -- and probably a lot more questionable, and we can't anyway have a special case for everyone out there.
So again, I don't really care either way. I'm fine with having Haiku tweaks in even if we'd rely on actual users to contribute it (same as I'd be happy with *BSD tweaks if need be, or basically any other OS different enough to require it, virtually no matter the user base -- yet, don't make me say what I didn't, don't create a fresh OS just to add support here :wink:); just as I'm fine with these kind of defaults being left to the providers.