Like Baozi said. The only units with mixed armor/noarmor that I can think of for the Romans are the Cohors Limitanei. Possibly also Equites Alae. I can't begrudge you for your opinion, of course, but I definitely take the opposing view. I really detest artifical uniformality and am not averse to mixed armor in a unit. In a perfect world I could make it so only the first three ranks have armor and the rest have a mix of armor and no armor, but unfortunately it's not possible. I do plan on doing similar things for middling tier Germanic units, at least perhaps before reforms for them. It'll help to distinguish a unit in the middle tiers that are better than levies yet not as good as higher grade or elite units.
All a matter of subjective preferences and interpretation of our limited information on antiquity, so nobody is right or wrong.
I'd recommend looking at tutorials on how to change Variant Mesh Definitions to see about fixing it for your own use/as a mini mod. It ought to be fairly easy as I have the names of say, a VMD for armor or clothing or whatever fairly explicit as to what it is.