Think crpcarrot and others nailed it. In past TWs the higher exp units were tougher to kill so you were able to keep advancing their exp. It was all simply a matter of fighting in enough battles. But in ETW, with no defensive value in shootouts, you get to a point were your tactics set the max exp your troops are going to get. Basically the number of enemy killed equals the amount of exp lost by your guys who died. You can improve it by meleeing more as that still uses a defensive value, but over time everyone will come to a point where they just can't seem to get more exp. That point is their tactics level. Unfortunately for me it seems to be 3 chevrons on Hard. =(

I have started to use the cavalry trick to draw off part of the enemy armies but feel kinda cheesy doing it. I'm also trying different army configurations in both makeup and deployment. Of course always trying to find a better defense/attack strategy. Hopefully I'll find something.