I think the origin of the troubles with emplacements are pretty simple.
Brace.
This ability is just BS incarnate, free, non doctrinal, with same downtime as uptime, 90% true damage reduction instant activated skill.
How the hell is such a concept tested and approved in a rts game? Theres simply no way of countering it, except looking at it go down for half a minute allowing the enemy brit to move their entire army to defend it and just repair it in your face at 0 cost.
The solution would be pretty simple, brace protects against arty barrages and explosives, not against direct assaults/fire. Would still make brace valuable for keeping emplacements in the game, but not make them indestructible 30 secs for free with no counterplay.
Brace working for only Artillery (which is extremely rare Early-Mid game) and Explosives (Even more Rare)? Wouldn't that be, in otherwords, pointless?
If this was to be done, two things need to be taken into consideration:
1) The Bofors is the only form of reliable AT Brits get early apart from the AEC (the faction's ONLY non-doctrinal Snare). Picking Bofors locks out the AEC. If Brace has no defensive applications, you will need to provide an equally effective AT Solution for the point it hits.
If the Balance patch hits as is, this is going to be twice as bad, with OKW having all its multitude of T0 AT Options invalidating Light/Medium/Heavy Vehicle play.
2) Losing Brace would mean British Emplacements would vaporise fast. They would need a Health increase/Armour increase to compensate for this.