Hi!
You seem to be a too good player for Athena

It's ans Ai after all
The British forces (even the AI ones) get pretty scary in 1776-1777-1778 with all those reinforcements, but if you know how to play your cards as the USA you can defeat them little by little or worts still, sneak around them and deprive them of their big towns and supply bases so winter and supply take a toll in them. I try to avoid using "gamey" tactics against the AI so things are more interesting.
Each campaign play pretty different too. As you WIA supply system is pretty unforgiving, so bad luck or a wrong move or two by the Ai can sometimes be devastating for her forces. But other time she pulls a couple of good move and things change dramatically .
Even after the British forces are not a big danger any more, the USA has to take the offensive and go for the Canadian and Western Objectives which is a logistical and planning challenge too. At least for than i certainly needed the French give me a hand with all those ships and regulars!
Using hardened activation can make things more challenging for you too. Specially when playing as the Brits whose leaders are not so active as the USA ones.
Cheers!