Climbing speed ≠ W/kg estimates.
The Jumbo guys set the 2nd, 3rd and 4th fastest times up Angliru in history, saying "well, the level of the opposition was low so it wasn't that dominant" rings false when five of the guys they beat
also set times among the 20 fastest ever on that ascent.
Landa was faster than 2013 Horner. Landa and Poels were faster than 2008 Contador. Almeida was faster than Valverde's best time. All of them were faster than Froome, Sastre, Jiménez, Menchov, Escartín, Purito or Cobo. It wasn't that the level was low.
Yes, the stage was short and not especially tough which might explain something compared to, say, the 2008 times which were in a 210km stage with multiple prior ascents. But since then we've never had a 150km+ Angliru stage, the 2011 and 2013 stages had easier run-ins and only the 2016 stage had a strong chain of climbs leading into the final ascent.
TBH this is the flip side, however. This is what we were told in 2012 too. "Oh, Sky aren't doing anything out of the ordinary, they're only dominating cos everybody else is focusing on the Tour. They might be dominating for five months*, but there's nothing ridiculous about it, because it'll be different come the tour because everybody else is preparing for the Tour."
Then they were just as if not more dominant at the Tour, and the same quarters were defending it as "well, Sky haven't been ridiculously, it just looks that way because the entire péloton other than Sky messed up their preparation for the Tour".
*actually, in fairness, Froome wasn't, he was riding like absolute turd most of the time until the Dauphiné when 2011 Vuelta Froome miraculously reappeared. Wiggins, Porte, Rogers and their like were going great guns all season though.