That is unrelated to my question. I'm using hinting and have everything sub-pixel-related disabled. If flutter does not support this, then flutter cannot look native.
Flutter uses Skia, Harfbuzz and FreeType under the hood. The last two is used by almost every other software for text shaping and rasterization.
You should open an issue if your font configuration is not applied, although on Android, iOS and macOS font hinting is not relevant, and I think on Linux fontconfig is used. I don't know about Windows.