yeah, a lot of times the a.i. will send either:

A)a bunch of tiny armies, that could be a threat if banded together. In my Prussian campaign, after I invaded india(there was a rebel province i took, just to have a bse in india.) stupid marathas DoWed on me, after being my trade partner for literally 139 turns. they then used some very elite royal indian infantry guards (using the AUM mod) and sent out about 10 of them to chalenge my army of: 1 landwehr, 1 line infantry, 1 company infantry, and 4 cannons.
unfortunately, they were not in the same army, so i hunted them down 1 at a time. though it is very satisfcatory to see them get ripped apart by shrapnel shot.

or

B) they send 1 large army of (usually) crappy troops, and once defeated, they have no backup army, or if they win a city, they stay there instead of pressing an ofensive.