This is the kind of thing that leads to an "uncanny valley" app, where things feel slightly off, or they look good until the OS changes something and Flutter doesn't keep up.
Disclaimer: I wrote that line :(
I don't trust Google to emulate a perfect UI among all platforms. I feel like they're generating too big of a workload for no reason, it's a big red flag. I think eventually they'll give up on emulating native controls and choose a unified appearance for all platforms (forcing Material design for everyone) as well as giving the option to customize. I think their endgame is to push Flutter as much as possible so they have Fuchsia developers, then let the other target platforms go unmaintained. Their language, their OS, their devices.