> flutter apps embedded in classical websites.
Sounds like Java applets.
Which mostly died from JVM startup time (Think 30 + seconds). There was other issues as well (security and UI issues mostly) but if you knew what you were doing, Java applets were not bad for the time IF the JVM as already loaded.
If you're trying to create a classical website, it's not the right tool. Use html and css. If you're trying to make a rich app, I'd bet on Flutter.
I'd be interested in seeing it become easier to make a combination of the two -- flutter apps embedded in classical websites.