The Esprit like the 20" wheeled SST that replace it (and is also lighter than the TSR) was not made in the same factory as the frames with a "shot-in" tube construction.
But this is not the real difference.
The "shot-in" tube construction provides a different feeling when riding the bike, you can feel this when comparing the Jubilee and the SST that otherwise seem very similar.
I also agree with
berlinonaut sating that the Moulton is not over engineered.
The Moulton Speed I have is still a unique design offering something that no other road bike can offer: the reactivity of the small wheels (same as with a Brompton), the speed of a very good road bike and a level of comfort+efficiency on bad roads that no other road bike has.