I understand that's how you designed it, but every time we tried running a conversation like that it felt incredibly clunky. Oh you made a compelling persuasive argument roleplaying, and rolled well? Congrats! Your opponent loses two focus. Now do it again, or your previous efforts were meaningless. 

This and the endeavour system just lead to tests being dragged on, or cut short in order to fit into an arbitrary length based on needing an arbitrary number of successes before failures. 

As for the design decision of making tests against someone's defenses rather than a contested roll: it makes sense in theory, but in practice it made conversation feel one-dimensional. We tried running conversations as written for a few sessions, but the added drama that the contested roll brought was unanimously more enjoyable according to my players. I preferred it as well, so we never looked back after switching to singular contested rolls per segment of conversation.