If you're already ignoring a big chunk of the personal interactions that happen in the game - NPC reactions - then why not ignore the delivery of the protagonist's dialogue, too?
I'm not ignoring the NPC reactions. The NPC reactions are vital.
I'm just not pretending to be able to read the NPCs' minds.
And no, we don't decide how a line is delivered. There is no mechanism in Origins to tell the game how a line was delivered, yet it certainly was delivery in a particular way in the fictional reality told to us by the game. It's like saying there are no toilets on the starship Enterprise because we don't ever see someone use them in Star Trek. An aspect of the setting that would be congruent with reality but only implied to exists can't be taken to not exist.
There's no inconguity. The only incongruity appears if the PC speaks without you knowing why, which is inevitable if you rely on the game to tell you how a line is delivered.
re: restrictions
How do you figure? Hawke and Shepard are much more strongly defined as characters than the far more vague protagonists in Origins and Inquisition, and as such they offer clear guidelines on what would be appropriate ideas about them and what not. And I've made tons of character-driven decisions in all the ME and DA games. I'm not sure I understand your issue here.
Hawke amd Shepard are much more strpngly defined, but not in a way the player can discern until it's too late.
I wanted Shepard to withhold information from Udina, but I couldn't do that.
I wanted Hawke to be civil when dealing with the slavers in Kirkwall, but I couldn't do that.
I wanted Shepard to be civil when talking to The Illusive Man, but I couldn't do that.
There was no way to construct a character personality in advance and then stay true to it. There was no way, moment to moment, to predict how any given line would be delivered, or even what it would say.