I'd say insufficient skill was a bigger issue that overall speed this season. And when the team is disjointed, failing to build rushes with a series of accurate passes, then it plays slower than it is. Stastny wasn't fast here, obviously, but he is very effective with speedy wingers as he is showing in Winnipeg. Sobotka is quick, but not especially fast. Schwartz was flying until he got hurt; when he returned, he was a step off his old pace. When Tarasenko gets frustrated, as he often was this season, he can lose a step. Brodziak isn't a great skater, but he became one of the more effective centers on this team.
When healthy the Blues had better-than-average mobility on D. Pietrangelo, Parayko and Dunn skate well and Gunnarsson is not bad.
I will say this: Vegas got the league's attention by rolling four lines with speed while forgetting the traditional model of two scoring lines, a checking line and an "energy" line. The league is getting faster all the time and the Golden Knights did more than their part to drive that. Thomas and Kyrou can skate, so they should help this team pick up its pace.