It is possible to improve the distribution and that is the thing being requested.

If you want to improve the distro go ahead. But it's fantasy that every distro will support every software => flatpak

The suggestion is not for all distributions to support all applications, it's for Debian to support system-wide disabling of telemetry in the software it does support.

They could compile Firefox with telemetry disabled however i would not trust those settings since even with that Firefox does plenty of unsolicited phoning home and has a lot of bloat.

I prefer to have a trusted third party (the distro) vetting updates to the software I install. But if you have the time and capability to vet all patches yourself then sure, you can use flatpak.