This is what the author was addressing with "It’s worth noting that Flutter for Web is currently in beta and the problems I am about to detail could be addressed. However, I believe these issues are fundamental to Flutter’s design choices so I feel confident in my criticism."
I agree, this is a fundamental problem they are probably unable to fix.
It was always my impression that rendering to a canvas was the quick n dirty way to get something running on the web, not the long term plan for flutter
I agree, this is a fundamental problem they are probably unable to fix.