I think Sagan is an outsider but he still can win the WC this year. He has beaten Kittel in a few sprints in the tdf this year and also showed on stage 21 that he can beat Greipel. The only rider who was basically always better than Sagan in the bunch sprints of the tour was Cavendish, but we don't know yet how Cav will deal with the long distance in Doha. He trained for the track this year which is probably why he was so strong on really easy stages but his climbing seemed to be worse than ever which might mean that he will also have problems in a long race like the WC. I think Kristoff, Bouhanni, Demare, Matthews, Viviani, and so on will probably be slightly worse than a Sagan in top shape but they are ofc. all contenders for a medal and might also beat Sagan if he doesn't bring his absolute A game to Doha.