And that is exactly my point specialized units like heavy assault guns should be able to counter fortification easier than all-around "heavy tanks" like Tiger and KT.
One proble, with your OP is hat you only mention Sturmtiger in specific. I can't help but feel like you fired it onto a mortar pit, got dissatisfied with the results, and then come here complaining about it. That's not wrong per se, but it would mean your argument is far too general given the specific circumstances.
Assault Gun units in this game have superior range, that alone makes them effective. But like I said, AT Guns and Mortars have this specific advantage as well. The only thing a mortar pit, bofors or even 17 pounder can do to a Jagdtiger is keep it spotted as it fires at you or you keep plinking away at its front armour. And that's only if the enemy is foolish enough to bring it within firing range.
Question: how bad is the situation you are presenting, and exactly what solutions do you have in mind? As said, heavy vehicles have the benefit of range and, mostly, armour, so they already serve as suitable counters. You suggesting they have tremendous damage bonus against emplacements? As in one or two shots? Have you tried these units against various emplacements? A single UKF emplacement using brace isn't exactly a valid observation to apply changes across the board.
Other options do kick in like offmaps and rocket artillery...
Another reason to not bother using heavy vehicles, offmap require only munitions and sight, and artillery requires far less CP, MP and FU.
That is if have chosen to attack a fortified position. If have chosen to fight elsewhere until you have better tools to deal with you can have plenty of time. Further more late game use of fortification should cause less time to counter them since the fuel cost to built them as an investment has less of an impact.
In that case, I can still win the game without ever deploying heavy vehicles.
If heavy vehicles are so effective counters to emplacements, then UKF opponents only need to choose those specific commanders, or do nothing but blitz to T4.
Lastly, no one's going to accept the view that Sherman Dozer would perform just as well as ISU-152. Not all heavy assault vehicles should perform the same as eachother. At least AVRE and Sturmtiger have shorter range compared with ISU-152 or Jagdtiger.
I agree with other detractors: these units already perform their role suitably. The only argument you have to make them better is because Relic's text says they are. Never mind the fact that what Relic says often has little to do with practical results (Relic says this game is super awesome, is that true?), but you haven't offered any practical suggestions: are you suggesting a Sturmtiger should one-shot any emplacement, even if it has brace? Because no one, not even the most hardcore OKW fanboy, will think that's reasonable.