I find most people making this argument haven't worked full time with one or the other.
If you're a larger company who can afford two teams/groups, or if you are working on something lower level like OpenGL or ML, it makes sense.
Having done both for multiple years, I can't understand when people think it would be faster to build separate apps. It's not even remotely close. You're swapping out doing bug fixes, platform specifics like push notifications, the occasional separate UI implementation, and distribution twice with doing _everything_ twice.
It’s more web than RN and depending on what you’re doing might not feel as native, but it’s pretty easy to make a solid app with it.
So when people talk about cross-platform on the Mac, for example, it's always some JavaScript abomination, or Java, or Delphi (yes, seriously), or Go.
How about going the other direction and getting Cocoa running somewhere else? GNUstep, Cocotron etc. Gosh, that would actually make sense, can't have that. Literally.
In fact, one company did. Apportable. Google bought them and buried the tech.
Hmm
There’s definitely a huge learning curve and some rough edges, but the speed with which I can write a polished UI in it is staggering.