Not really, no. Flat packs still need the host GPU, kernel driver and more.

I sometimes build software and opensource is easy for Linux. "Just compile once for fedora 40,41,42 and 4 Ubuntu versions, look how to build for Debian because the compiler there is 8 years old and then do that for very major update. Forever

Valve does not recommend that anymore.

And for good reasons:

Nearly all Linux native games I have from steam do not work any more. Glibc changes. Xorg gone. Other stuff. You would need to maintain and adopt constantly.

Having a product that advertises native Linux support on the storefront but requires Ubuntu 20.04 is nothing we or valve could want

Proton offers a stable surface, and decouples the dependencies