Delixe: *Spoilers*
.
.
.
.
.
I was under the impression they could come and go as they wished it's just that they choose not to associate with anyone for obvious reasons. This is the only reason that can explain the Aaravard being out hunting the Tal-Vashoth (other characters like the Viscount even mention they go hunting their rebels), the Qunari delegation that was kidnapped and the Viscount's son who was following one of them on the wounded coast.
*Spoilers*
.
.
.
.
.
They walk about the outskirts, yes, but i think Kirkwall itself it's a different matter, that was the whole point about the Viscount 'gifting' them the Compound. Sanctioned teams/delegations coming and going could do so under 'friendly' escort and for the more 'covert' stuff, assuming the Qun even allows covert stuff, they could always use small boats to leave the compound without going into the city. I guess another playthrough would be useful to try and pay more attention to some of these details and stuff overlooked the first time around, but sadly at my end that ain't happening.
In any case, i'm not disagreeing with you on the overall railroading thing, it's just that personnaly i thought that the railroading feeling in this particular quest as a whole relates more with the inflexibility of the Qun than with anything else.