Very poor performance under Linux

[Leif_-]

There's your problem. Dominions link to a different version of the OpenGL libraries than GLXgears do. Most likely the version in /usr/lib/ is the Mesa software-based version. I'm not sure how to sort it -- you can try to move all files starting with libGL under /usr/lib to a backup directory and see if that sorts it. It might cause some issues, in which case you'll have to copy the files back again.

I also notice that neither program depends on the libnvidia-tls library, so am I right in assuming that you haven't installed NVidia's own Linux drivers on your system?