As a non-cult-follower, I still have to say, he simply crashed. Possibly over confidence or possibly the opposite was the culprit, but caved under pressure implies you were in his skull that day.
I agree, and there were rumours of a faulty set of Michelins, which is not impossible either. Valencia has not been a happy hunting ground for him in general though, hence why he so wanted a points lead which Lorenzo couldn't surmount just by beating him there in the last race of the 2015 season.
I don't go for the Rossi only won because of advantages thing in general, but rather agree with what it was J4rn0 iirc contended, that he had the advantages that his predecessors as the top rider such as Doohan had as the top rider and arguably earned by being the top rider, and also give credence to another contention (Babelfish's, again iirc) that the SNS tires were pretty much a control tire for all the teams/riders who were competitive, with the caveat that there was an element of catch 22 in that you pretty much had to have the SNS tires to be competitive.
I do take exception to Hayden's title being detracted from, which that element of his fans did back in the day, and which he himself has now done imo twice, in the interview recently posted and in a similar vein in another interview a year or two back. I could argue if Stoner had been more focused in 2012 he could have won the title that year but he wasn't and didn't, and hasn't claimed that or any other title he didn't win to my knowledge.
There were certainly a number of things that didn't go Valentino's way in 2006, Elias getting the SNS tires for that one race among them, and it was a year of close to the most equal equipment through the field ever up to that time and for many years subsequently, which makes Nicky's win more meritorious imo, akin to KRJR winning in 2000, with Ducati having a competitive bike, 7 individual race winners and nearly another by KRJR who miscounted the laps, and Hayden who was an excellent superbike rider riding a great season that year on a bike and under a formula which suited him. Much though I liked seeing Bayliss win, Hayden may well have been able to win that last race had he needed to win it. Along with all this while Valentino had a team-mate with a very defined role ie to help Valentino Nicky had a team mate who was actively working against him and it appeared less than full support from his own team, cf Pedrosa taking him out absent which Valentino wouldn't have been in a position to 'give away' the title at Valencia. As has been alluded to if you re-watch that Estoril race Edwards was blocking Valentino's competitors as hard as he could.