My trader character also traveled without a unit across the inner sea and in one month got attacked two times by pirates, one time barbarossa bravly defeated them single handly, the other time they took 400 or so of his shiny coins.
It also didnt happen to me much, yet i figure its quite logical, both times ocured when i was traveling to a rogue region over sea.
Must have been al those deported Madinans from the civil war luring around Paisly and Port Raviel now.
Yep, they've always been scum.
PS, i dont think its overpowered at all and must say i like getting my characters robed once in a while for beeing to greedy not to pay for protection.