I generally share your reservations.

But as I understand it, proponents of alternative DTs are talking about a conditional PD where you know you face an opponent executing a particular DT. The fancy-DT-users all defect on PD when the prior of their PD-partner being on CDT or similar is high enough, right?

Wouldn't you like to be the type of agent who cooperates with near-copies of yourself? Wouldn't you like to be the type of agent who one-boxes? The trick is to satisfy this desire without using a bunch of stupid special-case rules, and show that it doesn't lead to poor decisions elsewhere.