It is. Seriously, how often did you get to use it where a normal stadium would suffice? The ONLY decktype which doesn't like Windstorm is RaiEggs. And both Raichu and Exeggutor only take 3 energy to take down should you run an average stage 2 Ex, or a low number of discards should you run Metanite, or 5 supporters in the discard pile should you use BanDoom, and the list goes on. Cessation Crystal is good for one or two turns before the wielder is utterly destroyed.
Small statistic. In the past 4 CC's, I had Windstorm maindecked (by advice) 3 times. In those 3 CC's I had played 15 matches. In those 15 matches I had exactly ONE situation in which I could use Windstorm, while I faced 4 RaiEggs. In the CC where I did NOT deck Windstorm, I got in 2nd.
Small statistic. In the past 4 CC's, I had Windstorm maindecked (by advice) 3 times. In those 3 CC's I had played 15 matches. In those 15 matches I had exactly ONE situation in which I could use Windstorm, while I faced 4 RaiEggs. In the CC where I did NOT deck Windstorm, I got in 2nd.