Designed around the worst case

The refit suggests that the baseline hull had room, power, and layout allowances beyond its immediate peacetime mission. In this interpretation, Starfleet planners expected an uncertain future threat and made it easier to remove laboratories and civilian facilities than to turn a purpose-built warship into something more flexible. Standardized conduits, distributed systems, and excess capacity would support that hedge against surprise. The third nacelle supplies wartime speed and redundancy, although separating the three units geometrically would make it harder for one attack to threaten them all at once.