The fact that you need to learn a niche language like dart just to make stuff in flutter seems to me like technical baggage I could do without.
It's also a pretty easy language to learn if you're already familiar with any other modern mainstream language.
You seem to think that the framework designers at Google just decided to pick a niche language called Dart to write Flutter in when they could have picked Javascript to write Flutter in. No. They decided to make the design of Flutter as a framework so clean and pure that they would have to work backwards to figure out what language it would need to be written in and then they created Dart.
At least that's how I like to imagine it.
Dart pre-dates Flutter by a few years and had failed (a couple of times) as a web development language before Flutter chose to employ it. Would Dart be around today, outside of Google if not for Flutter? Seems unlikely.
Flutter indeed did decide to pick a niche language, albeit one that was used internally at Google. Tim Sneath discusses it on Software Engineering Radio:
https://www.se-radio.net/2020/12/episode-437-tim-sneath-on-a...
My understanding is no one was using dart really prior to flutter due to that history. Though it was obviously pivoted for flutter.
I don't have an issue with any of this though.