Who's to say that they're not setting up more for Drest in future content? We likely won't see Dalmasca freed from Imperial rule with the third Ivalice raid, but Matsuno has said he would like to return and help out when this scenario is to be written. I mean, ultimately I think it's far too early to say that this questline has "no bearing on the plot." The plot is not fully presented yet. Wait until later to say such things.