I wouldn't necessarily lose sight of the fact that it was a particularly fast race. MWDS has never have been asked to go that fast before over that trip, and so was entering new territory. You might point to his stayers hurdle career, but this division routinely turns out the slowest races across the board (about 13% below standard class par, and frequently slower than that). He did however, win a fast run Arkle, so he's not without speed, it's just that he's never demonstrated previously he can win a fast race over the extra mile. As I've said before, fast times aren't run by 'speed' horses. A fast time is run as a result of banging out a series of fractions and doing so by the even distribution of ones energy across the race distance. Effectively, the fastest horses aren't the ones with the greatest acceleration, (which is more typical of the flat) but those which are the last to start slowing up; stamina in any other langauage.
As Dom says though, he travelled well earning the nomination at the half way mark from Norman Williamson I think it was?. For all intents and purposes he did appear to simply empty, which makes me think it was a stamina issue related to a fast pace. His performance bore all the hallmarks of a horse that gets caught out thus, though you tend to see it more with novices whose lofty reputations earned in slowly run races get destroyed when they're asked to go quick for the first time (often at the festival)
I know King has VPU in the locker, but to my mind (and certainly if I were the owner) I'd be thinking in terms of the Champion Chase, with its additional prestige, prize money, and the fact that it looks weaker than it has for the last few years.
It wasn't very strong last year, possibly evidenced by VPU becoming only the second 6yo in the races history to win. Obviously Well Chiefs departure meant that we will never know what he was capable of. MWDS on slower ground won the Arkle in a faster time than VPU, and even when weights are levelled off at 11.10 he'd still have beaten the current champion.
I too think it would be silly dismiss MWDS, he was beaten by Redemption of all things FTO last season, but I do feel that the staying chase division is particularly strong, and there are no hiding places for a horse which is only 98% up to the task.