I think that ultimately (and despite what they might claim) Flutter just isn't a web technology (it's not suitable for rendering to web). But that shouldn't necessarily take away from it as a technology for native app development. React Native is a little better at this (and actively on rendering better to the DOM), but it isn't great either.
I think that might have been true when the DOM was the only game in town. With the introduction of WebGPU support coming to the platform a lot of those arguments begin to fall apart pretty quickly.
