I agree totally. I have been checking the above two tools you mentioned as well over the last few days. Dart script language is pretty unreadable and will be nightmare to maintain. As for Defold, I like the active community and simplicity but they still have a long way to go from being a usable tool to build business apps. Corona SDK is still the winner here.
Have you checked out Unity?
Dart script language is opposite to unreadable. If well executed, ofc. Guess you didn't read it enough to understand it. I know this because when i started to learn dart/flutter I was blown away how hard it was to learn vs lua. But after one month reading tutorials they all talk the same and I was more comfortable with the concept. if you use MVP, MVC, BLoC, etc. you will be fine (clean and readable code).