Brace should be addressed and maybe part of that is reducing flame damage against emplacements but removing brace and maybe forcing some emplacements to be garrisoned to be useful. Don't know, that is something that I need more time to think about.
I don't feel that brace itself is the issue with the emplacements. Brace is annoying but it does end and the cool down is long; once you see an emplacement go on brace just wait with your mortars or what ever for a little bit then start to whack it again while brace is on cool down (you just have to bait them into using the ability).
The real problem is when brace is compounded with how stupid fast/easy the cancer commander can fix his buildings. Add brace + passive repair + increased armour means often you can't even do damage faster than they can repair it. Maybe if the passive repair range was reduced lots then it would be easier to target the forward command repair rather than the emplacement making it more fair I guess.