I've been using C++ to share code between iOS and Android for years and have come to the same conclusion. I developed the C++ code on desktop operating systems which was easier to debug, but once you move it to mobile then the debugging gets a lot harder (on Android at least).

The overhead of the JNI interface is quite a lot of work too. Luckily I had a UML model that I generated the interfaces out of, so adding JNI was just a matter of templating this out of the UML, but it was still quite a bit of work.

On iOS the situation has gotten worse in that the interface between Swift and C++ has to go through C, so if you are using C++ you need a special interface layer, which is almost like the JNI situation on Android.

So you have the trade-off of on one hand having two code bases (Swift, Kotlin) and the associated headache of keeping them in sync, versus the extra work of maintaining the C++ interface layers and testing and debugging on each platform. In the end I now believe that it is better to work with the platform native development tools rather than trying to share C++.

As far as finding developers goes, because of the rarity of using C++ on mobile there will not be a lot of developers with this experience. I work remotely and have found that any remote C++ work is very rare, Swift and Kotlin are a lot easier to find work with (it's still more difficult that you would think to get remote work of any type).