right about teh gladiators, i see you're playing brutii.
gladiators are indeed useless and were never used in an army i believe, except of course spartacus.
pigs are used against elephants, its scare the living jesus out of them
ballsita's are just a step up to onagers, they are indeed not great, but the only thing you have in teh beginning.
the dudes that can hide anywhere, probably those ninja dudes. can be used in your centre as melee or used for trapping when you are playing defense