SEO - maybe, but IFAIK accessibility in Flutter web app shouldn't be an issue (I just saw this comment from someone on Flutter team: https://news.ycombinator.com/item?id=24922849). They've been recently doing a great job in terms of performance (compiling app to WebAssembly) and size. I agree that Flutter web is not good for building websites, but for web apps, especially those "internal" apps used by a small group of users, it's a pretty decent solution.