Even with vanilla (1.08) I think allies / liege for players are pretty useless.
I've tried to claim a land title (Lyon in France) that once belonged to mine (somehow the vassal can swear fealty easily and switch his liege multiple times from another France duke to Byzantine empire) and Byzantine empire would send like 120k (initially 8k but once worn down they keep sending more troops) of armies crossing half of Europe, across Hungary & Holy Roman empire, just to save one land title of its vassal's, while if someone claims my county and invade my land, my liege(s) who stand beside my province simply don't care... at best they'll come out and fight off those revolting peasants.
I think there should be some kind of penalties doing such things. Attrition / low morale / supplies / lowering none-allied countries' relationships when crossing them, etc, otherwises NPC can just send their whole nation's armies to save one separated land title far away from them not incurring any negative effect.