About roman AI and such...
This has been discussed a lot lately.
I will just say this: I had a battle a while ago, mainly hastati in siege defence (no oil, battle was not at the gate, but behind it, so it got conquered) vs spear and sword suebi guys. I play - with factions i am used too - only on legendary. The three main fighting hastati units killed each between 150 und 300 in close meele combat, on legendary. This more than enough. On legendary even a levy can kick your ass
The reason romans doing extremly well on legendary is that their formations are really strong for the early units and lower exhausting, which is an important part of battle mechanic (which is a good thing).
The "problem" about roman AI is, and will ever be, the starting point of rome. I dont know who got the idea that the starting point is easy. If the AI or the player gets unlucky you will just have 3 factions invading your land from different directions. Also i have seen rome expand several times during my plays lately.
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I admit the difference between elite romans and babarians should not be that huge. Still i think, without formations, the babarians should be a bit stronger. But nothing too fancy.