So, the problem with the Dialogue mass is that the very name gives the impression that there's a Dialogue taking place between the Priest and the faithful. When altar servers say the responses, they're addressing them to God, and not dialoguing with the Priest. This is one step closer to redefining the Mass as an assembly of the faithful, in which the presider and the faithful are focused on one another, and interacting with one another, rather than as the Holy Sacrifice, where the priest and the faithful are focused on God. It's the same thing with the re-invented Novus Ordo "sign of peace". Faithful give each other THEIR peace, whereas the original sign of peace was actually CHRIST sending HIS peace out from the altar, where the sacrifice has just taken place, out to the congregation. When this is performed at the seminary, it begins with the priest kissing the altar, and so it ultimately originates with Our Lord and radiates out from Him down through the clerics, and then implicitly to the faithful. Our Lord's peace radiates outward from the altar, rather that Aunt Helen's peace being shared with Uncle Bob. And when done in the Traditional manner, it also reflects the Church hierarchy, as the peace follows the hierarchy of sacred ministers. Christ -> Priest -> Deacon -> Subdeacon -> other clerics.
So, when an altar server is saying his responses, he's actually speaking for the Church. Mass is the public prayer of the Church, and the servers are there representing the entire Church. That should by all rights be a clerical function, as that is specifically what clerics are, those who are designated to speak for the Church in that capacity around the altar. Thus, it's a bit different when you have clerics at seminary making the responses. I find that to be not inappropriate at all. In fact, I've argued in favor of restoring the ancient discipline where only clerics can take official roles within the Sacred Liturgy, and would have it that all altar servers should be at least clerics, and that the other Minor Orders would be restored, so that only those with certain orders can assume certain roles within the Liturgy. That would mean restoring the Minor Orders to be permanent rather than being merely stepping stones or milestones toward the priesthood.