Brace is strong and necessary, without it Britain can't head with mobile redeploying German hard-counters. Look t it like this, if the Soviets put a Mortar on the front lines behind sandbags and the German player sends a mortar after it the Soviet player can engage in a duel, which is equal since they're both roughly the same size or can redeploy.
A British mortar unit has no such option, so thus Brace exists. To be frank, Germany should find it frustrating to deal with a dug in British force, the Brits entire early game relies on it before their Armour comes in. Suggesting to nerf brace would be the equivalent of suggesting to nerf the USF's jack of all trades, the OKW's veterancy or the USSR's low manpower cost. By removing that gimmick you destroy the point of playing Britain which is to push up and castle. It forces the AXIS team to actually have to stay on the offensive. I know the AXIS have never really liked doing so but believe me if you stay aggressive the Brits wont have the time or MP to get to brace.
All the times I've won as Britain it's been because the AXIS players stuck to the same old strategy of pushing 50% up and building bunkers. Well guess what that Strategy is obsolete Britain doesn't give a toss about your bunkers and because of Brace your mortars won't allow you to hide behind MG42's and do jack shit. You have to be aggressive and believe me if you keep pushing the Manpower bleed Britain will suffer will force them to fall back, then resist the urge to dig in like you used to and keep pushing up. It's VERY hard to come back from that. If you try to dig in at 50% the British field defenses are designed to force you back, Brace is there to enable them, the British are the ARTILLERY FACTION, you shouldn't win arty duels with them and Relic designed them to resist arty duels.
/Rant
TL;DR: Brits are the arty faction and thus are designed to give the finder to arty.
Your post, and the millions like it, would make sense if all Brace did in its current state was protect from counter battery fire. But that's not what it does. You can pull the Brit's forces to the other side of the map, then quickly flank with a Panzer 4 to kill that damn Bofors that the guy slapped on the fuel point when he held it for 30 seconds. Brace Structure flips on, the Panzer does nothing, and the Brit's tank and 6 pounder comes rushing back, or his American ally shows up with a newly buffed Sherman. This exact scenario happened to me last night on Rails and Metal, and it cost my team the game.
Brace Structure is fine in concept, as a way to allow the Brit emplacements to survive a prolonged slugfest. I can understand that. But as it is, it is nothing more than infinite invulnerability. Either keep it under constant fire with your own arty to keep it Braced, when your arty needs to be doing other things, or concede that whole area to the Brits.
IT NEEDS TO BE MORE VULNERABLE TO DIRECT ASSAULT WHEN IT IS BRACED. It's as simple as that.