There are both advantages and disadvantages to the entire situation, on both sides of the Tribunal-Outlander conflict. Obviously, Outlanders are going to be wanted quite a bit, especially at the high levels, so in your scenario the mage may already well be wanted. But, he also may well not be, and since the Tribunal is not permitted to flag someone who is trying to retrieve an item, this won't always be the case. And if he *isn't* wanted already, even if he has defenders in his pk range, he can flee one room away and stand there sticking his tongue out at them. That's a big advantage over a Tribunal raiding the Outlanders, in which any Outlanders who are around can set up traps, ambush, lurk around in hiding, and do other sorts of dirty tricks in the forest before a fleeing asailant could retreat even for a moment. Like I said, there are advantages and disadvantages to both situations.

I can't say I am completely familiar with how manacles restricts each class, but I can just say that thematically, it can well be argued that mages, particularly Outlander mages, are more capable of being particularly disruptive to the sanctity of a city and more capable of evading punishment. Bards would probably be in this category as well, and if they were rendered incapable of using an instrument while manacled, (either unable to sing or forced to use 'a capella' depending on their level) I wouldn't complain.