My first playthrough... I have no idea that I can actually do all the side quests after stealing the Normandy until I "stumble" into the Armstrong cluster on the way from the Citadel to Ilos (a mere mis-click).... all of a sudden, much to my surprise, I'm into an argument with Hackett and no real way to turn down the mission or tell him that I'll postpone it until after I take down Saren.
You can't tell him you won't do it (or if you can, there's no way to know which paraphrase will do it) but you can still not do it.
That's a dialogue issue, not a pacing or agency issue.
If you leave the subtitles on and the volume turned down... you have no voice, just typed-text for both the PC and the NPCs (the equivalent of no voice-acting). If you really don't want to play a game as others write it for you... write your own. Turn the subtitles off as well and dub in your own dialogue for both PC and NPCs.
I don't want to write the line myself. I want to choose among the available lines, but with the paraphrases I can't do that, because I'm not allowed to know what the lines are.
And if I waste my first playthrough learning what all the lines are (and to do this properly I'd really need to document every dialogue tree), that means that when I finally get around to playing the game all the events have been spoiled for me.
That's a problem. I abhor spoilers. I want to experience the content for the first time from an in-character perspective, but I can't do that if I need go through the game once undoing all the paraphrasing before I can actually play.
My goal with turning off the subtitles is to eliminate the full line entirely, thus making the paraphrases themselves the sum total of the protagonist's dialogue. I don't want to know what the full line is, because that knowledge will colour my interpretation of amy NPC response.