But there are two stories. The plot about Saito and Fischer is the Macguffin, but it's also a roadmap to the real story, which is the Adriadne (?) and Cobb story.

And I'd argue that you're just picking and choosing which statements in the movie you wish to decide were true, and having stipulated that the movie is never presenting an objective reality there is no basis on which to make those decisions.

If the whole thing is a dream is there any reality to the idea of totems and how they work? No way of knowing. Is there any reality to the idea of limbo? No way of knowing. Is there any reality to the idea of projections and how they behave? No way of knowing. Each can be used or discarded as needed in pursuit of any theory as it can now be explained as a necessary component or just a lie used to achieve the predetermined goal.

I could just as easily, in my opinion, argue that the entire movie is a dream but the goal was to take dream researcher Cobb and get him break his ethical vows in order to commit an act of inception on Fischer and that actually the last scene after waking up is really the first time Cobb has been awake in the movie and his weird dream is making him uneasy as he goes through customs. After all, nothing in those final scenes explicitly mentions that he was on the run from the law. Maybe he was actually on his way back from a scholarly convention in Europe where he was waylayed by Saito and his crew.