.
Yes sure, I totally agree with you about ISU but in this case I still think that you have a huge advantage in teams games with a single sturmtiger and mates supporting you.
I think it's very map dependant. A map with lots of shot blockers (Ettlebruck, Minsk Pocket etc) makes it hard to spot a Sturmtiger without recon planes. A map like Steppes makes it very easy.
We shouldn't judge too early. It comes rather late and may or may not pay off. Its gun takes a long to aim which makes it hard to use against someone who spots it with recon units.
If it turns out to be uncounterable its ability to pierce through world objects should be removed.
Out of curiosity: would it be possible to reduce its damage when piercing through world objects?