How can you believe that the world #2 and arguably the current best HC player is not a big favorite to defend his points in Toronto? It's not like Nole is a #60 ranked journeyman that would have a small chance at defending his Toronto title. At the very least he is a strong co-favorite.
With the race this year being so close, being unable to try and defend 1000 pts could make a huge difference. Although I want Fed to end year #1, I still want it to happen fairly and without putting other players at a disadvantage, especially one that could probably have been avoided..
There's no "defending" or even losing last year's points in the Race, in the Race you just cumulate points and that's all, that's what the end-of-year will be about.
Besides, I don't understand your point : do you think Djokovic would be more of a favorite comparing to Fed in Toronto than in Cinci and the US Open ?
I don't think it's different : Djokovic can get his points wherever he wants, in Cinci or Toronto, "defending" or not "defending", last year's points get lost anyway and then you try your best to get points this year in all of the tournaments in which you take part.
Concretely, if, as I thought already a few days ago, Djokovic takes part in Toronto and Fed not, the player who is likely to get more points in this year's US Open series is Djokovic.