Yeah. I have 800 amp service which is basically always done with parallel 400 mcm or 500 mcm (depending on where it is coming from, since POCO doesn't have to follow NEC)
Within conduit, there is basically no other option. In free air there are options (750 mcm, etc).
Even if there were, you could not pay me to try to fish 750 mcm through conduit or bend it
Yeah, (2) sets of 4”C 4#500MCM #1/0G (copper) is typical for an 800A service. My electricians feel the same way as you do about anything over #500, usually for 400A we parallel #4/0 instead of one set of #500.
The NEC permits using conductors #1/0AWG or larger for parallel runs, it doesn’t forbid it entirely.