"if a technology like Dopamine can actually encourage retention on apps aimed at self-improvement, that’s an inarguably good thing." No, it absolutely is not. Some of most horrifying abuses in the history of the human race have occurred under the guise of "improving" other people for their own good.
Analogously, when someone designs a diet app, they're creating the boundary conditions of a new behavior pattern for users. Their use of Dopamine aligns well with their end user's goals: in the same way that you hold friends close because you know they rub off on you, so too should we think about our software. Having an app on your phone you chose to let close to your mind and behavior - to be a new venue of your thought and future self - is a decision about who you want to become. And if that app can use good design, a good interface, and persuasive tech to help you achieve your health or diet goals: you win.
That's an alignment of what tech wants and what humans want.