Buffing or adding a non-doctrinal unit won't make other doctrines more "playable". All doctrines are playable as none of them take away anything from a faction, some are just better than others and the best ones will always be played more than the weaker ones. There is no way to make even EVERY doctrine as the good ones will always be good due to doing better things.
The philosophy is, play good doctrines to win, and play weaker doctrines for fun, but be prepared to lose.
USF need better armour that is solved by selecting Heavy Cavalry, Rifle Company or Armour Company and thats why these commanders are better than the others and thats what I was saying
and as I said having a stronger non-commander armour unit would make the other commanders more VIABLE as in more likely to be used by players USF doesnt need it but it would be useful
With Tigers, Pak 40s/43s, Shreks, Stugs, Jagdpanzers and Panzers in the enemies arsenal you are gonna want tanks that dont die in 1-2 hits
USF is in a decent spot right now with all its non-doctrine units effective at what they do and can got the job done its just their late game is a problem which is solved by going with a commander that has armour units
You can say the other commanders are good and you had success with it but if your enemy knows what he is doing be prepared for a tough fight