If you watch VO throughout a game, you can see that the effort is there 85% of the time. He's really good, for instance, backchecking on the rush. He's pretty good at keeping up with the opponents and has a knack for breaking up passes. Once the play settles into the Sabres zone, though, he holds his position covering the point guy, but only nominally so. He never aggressively pressures the point, he just does a drive by and curls around, giving the point man a ton of time and space to advance the play.
I would say his game only lacks 50 feet, but those 50 feet result in too many goals. I'm also a little surprised that Donny doesn't correct that. If it's obvious enough that I noticed VO's poor point coverage, Donny has to know.