I have Hail Caesar, which doesn’t do this (much to the consternation of many gamer that wants it to!), but instead has two mechanisms that I think reflect it better. The first is the support ability of units (where units touching those in combat add to the attack) and the other is the drilled Roman troops, which allow retreating units to pass through them. I think this is a better representation than swapping out units or other oddities that I’ve seen.
Even Hail Caesar allows a republican player to take small units, which I find a monumental arse-ache to play against.
Yeah, that ‘list’ wasn’t well thought out, in my opinion, but it is only a guideline to point people who don’t want to work out things for themselves in a direction that is roughly historical.
The entire game system is a toolkit, which is its best feature.