Well take a look at it like this: The Peek of the Cardassian civilization could be during the Lost Era.
The sleeker ships coming about then and what not, and later on the Galor and the Keldon more boxy and less graceful due to the more utilitarian needs.
It was like that for the Roman Empire and their swords. In the middle or height of the Roman empire they used the Mainz style gladius which was gracefuly made, but later on the used the Pompeii style which is alot more ugly, but alot easier to make...
Interesting, no?