DPS wise Sturmtiger sucks. its all about that burst damage and ability to shoot though sight blockers.
Yeah, but bouncing AT guns at bit under 50% of the time would also make the Sturmpanzer a noticeably better AT meatshield in addition to the obvious DPS over "If the enemy isn't paying attention I will wipe their infantry. If not, I'm a waste of time and micro".
To be honest, upping the Sturmtiger frontal armour a bunch would actually be pretty useful for it since it'd be more capable of getting all things on legs (especially AT gun) to flee in terror of its approach more easily since it won't lose health as fast. If it fails to kill anything, it'll at least take less damage to repair and less time to threaten the enemy's infantry again. That could actually be a pretty useful niche role in large games, with a team to set-up around the opening the ST made for them.