Also noticed how the Scimitar, twice as big as both the Valdore-types and the Enterprise-E, mopped the floor with all of them? The Enterprise-D and Voyager got beat up plenty of times by ships bigger than them. The Valiant Defiant-class got the unholy Hell beat out of it by that Jem'Hedar battleship in seconds (remember Nog saying how much of a danger it posed to anything in, what, sixty lightyears?). And I don't remember swarms of smaller attack vessels taking down larger ships in the big fleet battles that much, either. It was mostly relatively small attack ships destroying the other small attack ships, like scriminshing destroyer screens.
Also, I tend to think that the D'Deridex and Valdore fullfill different roles. I view the D'Deridex as more of a anchoring ship-of-the-line or battleship, while the Valdore-types are more along the lines of frigates or cruisers.