You can kill him only at the beginning of the quest. You can't kill him after the car ride, the game forbids you to draw your weapon. You can't kill him in Zuleiha's house, see her reaction to the event, get new dialogues, and get the full completion of the quest.
You can either complete the quest or kill him and lose quest content.
I tried not to talk to him in the car and Rachel still said that V was a bad influence on Joshua.
I took Rachel's money and went to the cafe anyway. No new dialogues, no new development of the quest.
If you turned down a bribe and went with Joshua to the cafe, it doesn't matter what you say, Rachel still won't be happy. So why give a choice of dialogue if the characters reactions are the same?
So your choice again - to do a linear quest or lose part of the content without getting anything in return.
All of this leads to the difference in one short phone call. No real consequences.
By that logic, you can do no story missions and V will stay alive forever. And then you can call it a secret ending.
an illusion of choice would be that the outcome stays the same, it doesnt
1)kill joshua in car = quest over, get paid
2)don't kill Joshua, fill him with doubt, longer quest chain get paid less
3)don't kill Joshua in car, support him, longer quest chain get paid more, BD is a success
now, you are saying you want more, or different choices.
this is like saying ending after one date, breaking up after a horrible relationship, or breaking up after a good relationship are all the same thing, because yall didnt stay together anyway.