It never struck me as a believable upgrade.
Then again, nobody in the episode claimed it was an upgrade.
From what we heard, the likely explanation is that it's just a pair of crutches and a neck brace to keep the overworked, broken ship in action as per Admiral Riker's whimsical orders.
Plus, it broke the convention that nacelles always worked in pairs
Naah. We had no real reason to think the four nacelles of the Stargazer
worked in pairs, or that the single- or triple-nacelled ships glimpsed on computer screens in the movies would have been only half-built. The future E-D was the third three-naceller seen on screen (not counting the barely glimpsed corner of an image of a Franz Joseph Federation
dreadnought in ST3:TSfS, but rather the up-and-center views of a Greg Jein Niagara
in two TNG episodes).