? AT was useless, or at least under-used, because there are far more soft targets than hard, and Arty's high SA values meant that even halving it vs Hard targets left it pretty effective. Having Pen on AT and none on Arty. Narrow focus is only a problem when a generalist unit does the job just about as well and also has other uses.
Edit: Reading further you seem to be basing your position mostly on hardcore MP games where things may be different.
I appears i didn`t explained it clearly so let me try again.
There are two units with high HA. One of them is slow, soft AT. The other one is hard, fast, TD. Since both have miserable SA, they pretty much both have to be directly deployed against armoured formations, in which TDs are way better than AT, due to spead, and TDs provide their divisions CA, that is always usefull, even if division fights soft targets.
This leads to TDs absolutly making AT useless under pretty much
any circumstances, as long as price and stats are realistic.
That is pretty much what is the problem with AT.
Again, AA, same problem, there just so few planes units, compared to divisions, that having AA is pretty fruitless, since you either need to build a lot of it, and sacrifice your ART support, or you end up pretty much never using it against planes.
Also historically AT and AA were not deployed in dedicated brigades, unless asigned to corps or army level.
They are just way too consentrated for divisions, and cover too small aeria. there either needs to be some mechanism of assigning them higher in comand, but i do not think you will change the combat system radically, so what i would say would be better:
Delete AT brigade, and let all infantry brigades benefit from AT tech directly.
Instead of AA brigade, introduce self-propelled AA. Since your armour is a high priority target for aviation, it makes sence to protect and suport it with AA, and AA brigade is just way too slow to use it that way.
It would neatly solve the entire problem with brigades.
Also, would you think about adding AGs?