I think he would be useful to keep banners out of the picture and any mounted heroes who are on the verge of charging. Also, never under-estimate nature's wrath. That spell once (yes literally) won me a game.

I must admit I haven't read the full SBG rules for the Stormcaller yet so some of this may not be directly applicable, but based on what I have seen and also what's posted above…

Natures Wrath really is one of the best spells in SBG. Well timed, you can knock over a host of enemy models then charge forward with your own and do devastation that they may not recover from. Just try to focus it on an area of enemy models without a Hero that may resist.

As for any push-back style ability, it's great under the right condition. I love the Wood Elf Sentinels in SBG. Their Song that lets you control a model is a great way to break up a formation, relocate a banner where it's not effective, or get a Troll just far enough away where you don't need to worry about it that turn. Additionally, if you can get a Hero even a little out of the way at the right time where it can't bring Stand Fast into play on a broken force you can see the game handed to you by a series of failed courage rolls.