Consider -himem for example. -himem doesn’t do anything unless your system has less than 62 MiB of memory. It seems pretty unlikely that a player would try to run a modern version of Descent 3 on a system with less than 62 MiB or memory, and if they do, then it’s probably fine if the game runs in low memory mode.
There’s probably at least a few different command-line options that are no longer relevant, and it would be good to remove them.