You almost never see anyone use this effectively, if you now what your enemy is trying to do it is easy to defend against. Also the ability stops when you reconnect your territory + 1 cache destroyed this entire strat.
IRstg as commander ability should work on most OKW infantry like USF LMG
that wouldn't fit, when you unlock the IRstg most of your volks should already have the stg upgrade. And you probably have a shrek or minesweepers on your sturms. It makes sense to only give an elite unit this special weapon
Apart from other nerfs, it should be immobile while reloading. Right now can take its time repositioning and staying close to the front line so it can fire again as soon as possible.
Also watch from 30:42 and on, for the effort it took to destroy the second Sturmtiger.
Bringing back movement disabled when reloading + lowering its total health should be enough to balance the ST. If there is still abuse after that, you can always look at lowering the damage output. About the replay: if he hadn't lost the FF he would have easily won
Related to topic:
Sturmtiger going in blindly against two ZIS-3s and one SU-85. the SU-85 misses at the end, but it had enough health to survive another shot
If you place your AT guns that close to each other you deserve to get bombed.