What is your specs exactly?
Which settings are you running?
What mods are you using?
If you're using mods that increase unit size, variations, more civilians, longer draw distance and other changes or graphical effects and filters. Then ofcourse you're running it worse than the vanilla game or Rome 2.
Also, Attila has some new graphical features that Rome 2 didn't have. Either they are quite demanding, or since they are new maybe they haven't optimised them just yet. Attila also uses bigger textures, well not bigger but les compromised i believe so they use more space and abit more demanding. It also has proper AA, which Rome 2 didn't have. And it has anisotropic filtering that actually works, Rome 2 only had the option but it made no difference XD
I don't have my gaming PC around me this week, but i did notice a small perfomance drop in Attila everytime a new patch hit
