Mr. Laser Beam wrote:
But even then, the Defiant having a dedication plaque in the same spot as Enterprise is a retcon as it didn't have a plaque in The Tholian Web.
The only reason that last bit is true is because of budget. They didn't have the time or money to do that in TOS, but it can be assumed to be true nonetheless.
But lots of things are still canon even if the decision to do it was because of time or money.
As far as the type/class explanation, its as good as any.