Take out the engine failure and Rossi is still behind in the points when he was ahead last year, JL is usually really good at the end of season tracks, and won't I think repeat an error like Misano 2015 if he is leading the title race rather than trying to make up a substantial deficit. Sure he can have a mechanical failure himself or be taken out by the error of another, although the way he starts takes him out of the range of most of the torpedo artists.
I actually give Yamaha the benefit of the doubt as to whether they will offer Jorge equal support which is one complicating factor, particularly since I expect MM to be close enough to be a threat to a Rossi/Yamaha title as well as JL. Not supporting Jorge this year might cost Yamaha their only chance of a title for three years, given while I agree Rossi appears fast enough this year it is a gamble that he will continue to be aged 38 and 39, and not a bet Yamaha really intended to make imo, as well as it being unlikely that MM will have bike problems which sufficiently hamper him over that period.