so I think i found a big problem, in the troop tree i found in reports menu it says that 'roman legionaire' has 200 proficiencies, however every level above that has either 100 or 125. It also shows these numbers when you talk to a unit and ask him 'tell me about yourself' to see his stats.

So basically if you level up your legionaire, he gets weaker, and even the armor and weapons hardly get any better. As it stands, leaving your romans as plain 'legionaires' puts them on par with roman centurions in terms of proficiencies.