I recall that the app Rows had their desktop version written in Flutter and it was extremely fast, able to render billions of rows as a spreadsheet, so I don't think it's a framework limitation but it is likely that Appflowy is not very well implemented.
Well, I'm yet to see a fast block editor implemented in Flutter (with proper RAM use as well). Another one is Super Editor[1] which is the editor from the Superlist app[2]. I didn't properly test it cause there are no builds. But the web version[3] hangs when I try to paste the text of War and Peace. I would like to test it properly one day.
