How does this sound for an idea. From what little I know about hull types I think it would be doable.
Leave the escort class that you start out with alone, then as you advance in ship construction tech, say level 3, along with the destroyer hull you discover an "enhanced escort" class hull. This would be the same size as a normal escort hull, but with the added abilities.
You could even advance it gradually. At level 3 say the enhanced escort gets +1 speed and some supply capacity, at level 4 a new escort class with +2 speed and more supply cap.
Explain it as better shipbuilding techniques allowing stronger structures with less mass in materials giving them more acceleration from the same engine power.
(Someone with more physics knowledge than me will have to tell me if thrust to weight ratio is applicable to to ships operating in a vacuum.
)
Geo