Its fine the way it is.
You just need to either support it, or use it to support you, you can't expect it to move in and change a battle on its own.
That the thing, it changes battles entirely on it's own. It can 1 shot medium tanks, wipe out entire blobs, it instantly kills support weapons. The problem with the Sturmtiger is that the micro required to use it is very high; making it unattractive.
The fact it's the least built unit in the game by a fairly significant margin is pretty telling. And it's funny because it is an excellent unit, but just pretty much unviable for the average player.