The reason to host a repo regardless is to enable easy auto-updates - and I don't think you can call this bit "smooth and simple" on Windows and Mac, what with most apps each doing their own thing for updates. Unless you use the app store, but then that's exactly the same as repos...
Only if you're using a distro that doesn't come with it preinstalled. But that doesn't make it distro-specific?
> And now I have to host a flat pack repo and get the user to add my repo if it’s proprietary software.
You don't have to do that, you can just give them a .flatpak file to install: https://docs.flatpak.org/en/latest/single-file-bundles.html
The reason to host a repo regardless is to enable easy auto-updates - and I don't think you can call this bit "smooth and simple" on Windows and Mac, what with most apps each doing their own thing for updates. Unless you use the app store, but then that's exactly the same as repos...