Yeah, this faction so far is pretty lacking in infantry based AT and people will need to bear that in mind in their subsequent choices
So far we do not have mines or persistent AT of any kind; so we are entirely reliant on fausts as a snare.
Something else will have to come along and kill stuff
I don't think that's an issue, as Pak40 is a lock to win the AT gun vote so any fausted vehicle will be dead meat anyway, the Faust+Pak40 combo works great for Ostheer AT needs and it will work fine for this fantasy faction as well.
As far as this upgrade goes, IR STG gets my vote as a garrison clearing option and wiping AT gun crew in late game situations.