Fnatic have an IGL with most events wins in the world, they have two other players with 5 combined Major wins, one of the biggest up comers and the Twist who is about the same as Flamie according to you. That doesn't make them a favorite.
Astralis have won to majors in a row, shouldn't they be a bigger favorite?
Liquid is ranked #1 in the world and have not lost an event for like 3 months. Aren't they bigger favorites?
Vitality is ranked #2 in the world and have more or less only lost to one team over the last couple of months.
ENCE haven't won much but they are high ranked and a great team that only lost to a few teams and have been known for big upsets in big events, currently runners up in last major.
There are about 10 teams that show more promising CS that are ahead of Na'Vi coming in to the major unless something drastically happens to the CS:GO scene.
For me in order of probability I'd say: Liquid, Vitality, Astralis, ENCE, Furia, Mousesport, G2, North, Renegades, FaZe, NiP, Fnatic... And then Na'Vi. Just by watching as much CS as I can for last two years!
Na'Vi is an upset and besides the three first teams I mentioned all are upsets.