Let's just say there is a "top" sprinter who wins 3 of the Category 1 stages and finishes 2nd in two....assume other one goes to break.
They will get 210 points for that.
And let's say that Sagan gets two 3rd places, two 4th places and a 5th place in those stages.
Sagan will get 92 points for that.
Now let's look at the medium difficulty stages (Mur x 2, cobbles, Rodez, Mende and Gap. Even if Sagan was to get two wins, a second and a third from that, it doesn't net him a massive pile.
Sagan would only get 91 points for that.
So it is likely that Sagan will have to make up around 30 points on the strongest of his adversaries in the intermediates. And given that in this scenario the dominant sprinter may actually go for green, he will be losing points in a lot of scenarios, when Cavendish sprints the intermediate for (say) 5th and Sagan maybe gets 6th.
Of course, if Cav, Kittel and Kristoff share the wins or if Kittel dominates but doesn't go for green, Sagan will be the most likely winner of the jersey. But I would think that Kristoff or Cavendish will win it, not Sagan.