One would think this a standard occurrence in space warfare: adversaries would seldom be technologically matched, as they wouldn't even know about each other, let alone the military capabilities of each other.
Space warfare? Yes. Trek warfare? As you yourself assert ... nope.
As for complete ignorance of Romulan combat capabilities, such would be far more likely if the UFP and Romulans did not have the Klingons, with whom it's strongly implied the Rommies retained an adversarial relationship throughout their isolation from the Federation, in common. I tend to doubt the Empire would have allowed its allies to remain entirely ignorant of Romulan developments in armament—not when they were probably eventually hoping to catch the Empire between Klingon hammer and Starfleet anvil.
Dramatic license is still very much a viable alternative.
Alternately, it may be that a relatively minute adjustment to Starfleet shields would have evened the odds immediately—as occurred with Jem'Hadar warships once the Dominion War began.
Now there's an interesting question: Did Starfleet Intelligence withhold knowledge of the shield adjustments necessary to repel Dominion polaron-based weaponry for days, weeks or even months before the conflict began, so as to goad the Dominion into attacking what they believed would be a nearly helpless adversary? Did they sacrifice a few or even a few dozen vessels in the hopes of saving thousands more?
Interesting ethical dilemma.