So, let me get this straight.
Someone's miffed because, canonically in TOS: The Tholian Web,
the dedication plaque on the Defiant
bridge said "USS Enterprise", but that was retconned for ENT: In a Mirror, Darkly
From what I can tell of my DVD copy of "The Tholian Web" and the TrekCore HD archives, the Defiant plaque is in darkness and too far away even on HD to where you can read it.
The USS Defiant in ENT can be a "Constitution-class" as there is no evidence that it cannot be.