Yes, that’s expected. It actually does damage to defense, and saps MP by twice as much (and of course, knocks the target back one tile). It doesn’t have a lasting effect, so the MP hit is really against their “saved up” MP. In other words, if they have 30 MP left and you hit them for 18, they’re going to lose 36 MP which will put them at 0. Their next turn, they will still get 50 MP back – but instead of having 80 MP, they only have the 50. So it’s more of a utility attack – push them around, knock down defense and MP.
ok, I think then you should chance the describtion of the effect when it’s executed. Right now it is the same as if it does direct damage (like jarring, rending and so on). There are other actions with similar effects as wind-tunnel which should take the same new diction… I guess you know those action to be considered better then me. With such a change I think it would be much more informative than right now.