I think the problem woth brace is it offers a HUGE buff to defense with no real downside.
The downside is it temporarily takes the emplacement out of the fight, so you have a window to punish his supporting infantry and give him bleed that way. Or if his force is strong, pull back and wait to push with hopefully indirect fire when brace wears off. Also that its left vulnerable after brace wears off, obviously.
When you face most strong units in coh your always going to need several counters combined, so a tank needs snares, ATG, maybe mines too.. most counter problems are not one dimensional.
Given that emplacements can not move, they are very vulnerable to thought out strategical counters. You can say that it takes little micro or skill to have an emplacement locking a portion of the map down, but the skill and micro comes in defending from a well executed attack on an emplacement.
In the late game of course there are some arty strikes that will just nuke them, which is why its nice to take railway arty or zeroing arty vs brits, but before that stage it should need a combined effort to take them down.
Bonus tip: If you are barraging a damaged emplacement, place the barrages on the rear egde of it where your likely to kill any repairing engies
MHT is less effective than you think.
First off all the weapon can easily miss the shot (scatter) if you fire without vision
Second a un-braced MP will drop to around 1/3 HP even if it get a direct hit
Third a braced MP will laugh at wasting 45 munition in causing around 25% damage.
This isnt Mortar Half Track Hero... hopefully you have an army which is supporting and protecting it, providing spotting and why on earth would you waste an incendiary round if the emplacement was not just about to have brace wear off. The standard barrage is probably enough to make him brace