I'm not even sure Go would do better on image size. Tree shaking does wonders here.
FFI is quite a PITA, though. Soomer or later you will have to interface some platform libraries, and Dart doesn't make that easy.
And here's a 500-line version of the Kilo console text editor built with Dart: https://github.com/timsneath/dart_console/blob/master/exampl...
Unlike the original, it runs on both Windows and UNIX-based operating systems.
To be fair, last time I looked into dart, the idea of FFI was ports, which was too overcomplicated and undercapable, if you needed something like Gtk or Vulkan. Looking into it now, I see the dart:ffi package is shaping up nicely, so I will have another look at dart again.
But even if not, if there is a way to (given might be slow and tedious) to compile what would've been flutter_engine.dll statically linked to your main (host) app, and maybe somewhat hinting here is how to find the "GetProcAddr/dlsym/etc." functions - if one is to look for them.
Further on, the generated from dart .so file can be embded (as resource? or slapped at the end of the binary/.exe?) + slapping all other resource - resulting in single app :)
I know it's possible, just not so easy to support it (I guess). It's similar to have java/python can be packed into one executable with all C/C++ ffi functions they call (at cost of some build time and effort to achieve so).
Then you'll have killer platform for video conferencing (zoom, bluejeans, etc.), messaging (slack, etc.) - and just single binary to deploy.
(Oh, on top of that slap a web server into it, and make it that if called with specific command-line option, now it acts as web-server, and the app is visible through the web).
This is what made me nope out of it last time I experimented with a Flutter module in my app. I'm still watching it closely though as it could be a great fit for other projects.
dart:ffi (https://dart.dev/guides/libraries/c-interop) is a recent addition to Dart and from where I stand it's a decent FFI system.
Maybe not as good as PInvoke in C# or ffi in luajit but better than, say, jni in Java (and any other FFI system that requires you to write glue code in C i.e. python, ruby, nodejs).