Ok, that's reasonable. Thank you for your upfront starting agreement. I obviously have some real emotional attachment to the issue of whether users have agency or not, and this has been a really hard time for me, and hearing some recognition of the jeopardy as relevant is really touching, thanks.
I had kind of assumed Flutter was performing fine/native-ish, it just didn't look native native. Different people will feel differently about the importance of native purity. I personally (with apologies) have seen native as a bit of a negative in general (with concerning privacy, dark patterns, & no observability/extensibility), and that's made me care a lot less about React-Native & Flutter & the like there. But if Flutter's really running bad too: that's embarrassing and not good, straight up!!
However, two things. The first is a repeat: it won't always be bad. This team is going to make this fast. There aren't real encumbrances to that happening & it will, is what my reading of the tea leaves says. Mostly gut feel, yes, but the plan seems solid. On the web, they're only just getting WebGPU booting, and still using older Dart VMs rather than actually compiling to wasm, so the web in particular is just barely getting started, but I'd expect the mobile situation has gobs of tuning potential too, and the team seems capable & smart & like they have the mandate to bring it. Their new Impeller optimizations to underlying Skia are just landing & already should help a lot, for ex.
The other point I'd just raise is the Electron/Slack problem. People all assume Electron is unbelievably awful & slow & terrible, because they used Slack a couple of times & saw it responds slowly. When an app is bad, people tend to blame the framework. Electron is not without sin, but there are examples like vscode where it is quite snappy & fast & universes more featureful & expansive-in-purpose than Slack. No matter what your development target, it's possible to make slow & bad apps.
I have no real insider knowledge of the Flutter app situation today, the lay of the land, but I'd caution too much against using current bad apps as an indicator of what to expect, caution against letting current experience too deeply/permenantly shape our belief/disposition (lest these form convictions which lead us astray from the truth everyone else experiences). More than UI, issues like Client-server data models & algorithmic complexity are woefully under-considered everywhere. Few businesses have a chain of command that speaks the tech language well enough to keep the ship from bottoming out or from not just rubbing along the seabed as it travels. It would be unshocking in the least to me to find a bunch of the big name Flutter apps are at Slack levels of quality internally.
Then again, maybe it is partially or all Flutter's fault! Maybe I'm wrong and it stays terrible forever! But the Highest Form of Disagreement is to assume these problems are surmountable, and I don't see anything really strongly technically impeding success (if having native widgets isn't somehow a requirement).