I was under the impression that originally the Reliant was envisioned as a sister ship of Enterprise and that the differences between the two ships would be minor, but then they realized that it would be hard for the audience to tell what was going on if the ships looked too similar so the new model was designed to be a squatter up-side-down Enterprise, essentially. I'm omitting a few steps of the design process, obviously, but I can totally accept an early draft describing Reliant as the same class as Enterprise and mean it in the usual sense.
--Alex
--Alex