I think they're pretty fine, after using them a bunch with the nerfed fire damage.
I wouldn't change a thing. Cost wise they are very cost effective and if you made them any easier to keep alive then they would be unkillable in the hands of a good player. The 17lber in particular is an extremely cost effective counter to vehicles. (2 shots panzer iv, 4 shots tiger)
If the emplacements get overrun, brit can either brace for a few seconds to muster a defense or lose them very quickly, as it should be. You still have to defend your emplacements with other units.
Pretty much right. But i think they are pretty much easy to keep alive these days, if you just have an AT gun near a Bofors, tank can only drive in to get some damage, bofors survives, maybe an addional vickers and you have a very good defense. I'd say if you need to do something about emplacements, let brace not take that much damage away from the attacks, maybe 5% less bonus to damage taken away, because it can be really punishing fighting against a emplacement , for example road to kharkov or crossing from north behind the trees towards bottom fuel, you waste a lot of time and it will not die.