ST was hideously broken (not in a good way) for a very long time, so it's stats weren't really tracked as it wasn't . Now that it is in a usable place, it may need tweaking.
Keep in mind, the most similar other vehicle, the AVRE, is CP 9 I believe.
We might get 1 more patch.
As an OKW, I would even accept 20 CP in exchange, Sturmtiger for the AVRE.
But the best solution would be to kick both units out ... fun factor equal to 0
For me (as a mediocre player) 3 out of 4 games are lost if the Brit arrives with the AVRE.