For those pesky random executables there's a couple of escape hatches -- buildFHSenv and nix-ld. This is also predicated on good provenance of the executables in question. One should probably not even ldd sketchy binaries:
For random binaries, autoPatchelfHook works miracles.
For better or worse it was a positive experience, especially when you usually already have a pkgbuild to go off of.
Also linking things to /usr/bin is done by the fhs which uses bubblewrap, not steam-run.