It seems companies are sort of mandatory after all, since the most junior army officer rank you have is Major, which isn't enough to command a battalion (Lt Col).
Command levels appear to be out of whack, though, if a Colonel can command up to something like 80-100 thousand troops (if the Ground Combat Command value corresponds to men under them).
Ranks can be renamed, but apparently not removed, so I'm not sure what'd be the consequences of reshuffling nomenclature to make command figures more sensible.