Gyms are boring. Cardio in gyms is incredibly boring.
Trying to beat my highscore on Holopoint whilst hologram samurai rush at me and I'm dodging missiles flying from all directions is not boring.
( And now I'm developing room-scale VR games, that goes double.
I'm currently covered in sweat in the middle of a work day after spending an hour balancing a miniboss in Left-Hand Path (http://store.steampowered.com/app/488760). )
There's a big benefit gap between working up a little sweat playing a video game in your living room versus doing actual weight training at a real gym. They are no substitutes.
Working up a sweat playing a game is more than most people do and will already bring benefits. It's a whole lot better than nothing. It may become a catalyst for better things.
And, yes, weight training is not going to be replaced by cardio, because it's weight training... it's not like every person who exercises does weight training, there are quite a few pure runners on here.
On the "better things" point: I also weight-train, I've studied Muay Thai, boxing, and a number of other martial arts, and I was an athlete in high school.
Judged by those metrics, some Vive games are still pretty decent exercise. They're not "equivalent to heavy sparring" intense, but they're a solid cardio workout.
Vive room-scale exercise can be rather more intense than you might think - see https://www.reddit.com/r/Vive/comments/4wtp3p/vr_fitness_50_... - or possibly I'm just bad at the games and substituting energy for technique :) .
What are you basing that on in terms of intended outcome?