Quote Originally Posted by mighty_rome
I haven't seen any satisfactory explanations yet, probably because there aren't any; the late Romani units are underpowered whether you want to admit it or not.
Underpowered ? Where ? If you ask me they're pretty much exactly what they were historically: disciplined professional grunts, well trained to fight in a certain (quite flexible) tactical system, solidly but not exceptionally equipped.

They were never all-around supersoldiers; the Roman commanders worth their salt knew it, and plugged the various gaps in their expertise with auxiliary specialists as well as padding out the by economic necessity somewhat low numbers with allies and auxiliaries. Properly deployed and commanded by a leader up to the task they certainly won wars often enough, but also often enough entire sections of a line might collapse in a rout and/or the Roman armies have to conduct bitter fighting retreats back to friendly territory. Green, inexperienced troops weren't ultimately that much better than anyone elses' (what now often noticeably better equipped than the rank-and-file of most other armies), and tended to need the example of grizzled veterans or the personal attentions of a respected commander to not turn tail in a tight spot.