It is quite interesting that you say you experienced the opposite — yet you actually confirm that flutter does not deliver on its main promise.
If that still constitues a success for you I have to conclude: your other projects have simply been worse.

From my perspective you do something that many unprofessional teams do: Declare anything as a success — no matter if initial goals were met. A former team of mine released a flutter rewrite. instead of 3 month it took them 2 years. they decided to axe several beloved features as they werent able to code them in flutter. It took them 8 times longer and they delivered something that was in the eyes of the users defunct, yet recently the PM told me, that he considers it a success — I call it disaster.

Your argument that otherwise more developers would be needed in platform teams: How stupid do you expect your coworkes to be? Can they really only work on one platform? In a professional environment you choose the right tools for a job — not the tools your coders are willing to work with. If a coder cant be asked to work on different platforms and in different languages and cant be bothered picking up new skills, I would let them go.

The first thing you highlight is the debugging capabilities. My response to that: Just write code without bugs. but to do that you need to simplify your project to the maximum (please refer to my articles: https://decodemeester.medium.com), but flutter is an additional complexity. You cannot fight complexities with more complexities and expect to win.