For me, if it's on screen, it's canon...no matter how much I disagree with it (*cough* Voyager *cough*). Of course, I love Enterprise, so that's not a problem for me.
I agree that NX-01's armament is probably so state-of-the-art that very few ships share her capabilities (and in the Romulan War, most of the combatants will be less capable than the NX-class, and vastly more numerous).
Case in point on "disagreements": Voyager established that there appeared to be little effect on the American lifestyle in the late 90s during the Eugenics Wars. The on-screen evidence allows me to say that the Eugenics Wars were mostly "foreign" wars that the US may have been involved in, but the nation was never (or rarely) really at risk.
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz