I would guess a change to the Brace mechanic is required - make it reduce damage only from indirect fire. Once this is made, I see no problem with the Brit player shutting down the functionality of the (very high upkeep) unit in exchange for surviving ISG / mortar bombardment. Once functionality is disabled, ground forces can move in and clean it up. That to me is tactics.
I think this wouldn't work because it leaves emplacements extremely vulnerable to ground alpha strikes. A couple of focused shreks would be enough to instantly remove a 400mp investment with minimal losses. There'd be minimal counter-play involved there as well.
It seems to me like the main problem here is brace functions too much like a hard-counter. If it's not active, your investment disappears too fast. If it's active, nothing can scratch it. If both the structure health and the dmg reduction bonus of brace are normalized, I think we can end up with a much better situation for everyone. The Brace bonus should be reduced, the base health (and armor?) increased so a concentrated attack that isn't repelled can take out the emplacement in a reasonable amount of time while also allowing ample amount of time to counter prolonged indirect fire from a single source.
In short, I think emplacements should function more like OKW structures. They're durable enough to sustain prolonged indirect fire but not enough to be careless about leaving them undefended for too long.