An Escort is designed to travel with cruisers and destroyers ect to provide fire support, just like the real navy. It would be used for Diplomatic missions where the probabilty of conflict would be high.
It was a rhetorical question.
Also the Defiant wasn't bought on line till the domion threat reared its head...
Only because of design flaws and "reduced Borg threat". Who knows how many were built. We only know of the Defiant and the Valiant.
The Defiant didn't come into its own, until they let Worf and the Chief, have fun with it.
After the fixed the warp overpower issue, and added the ablative Armor, and other Klingon inspired goodies.
It was one little vicious ship.
If I remember correctly, they said it had the fire power of a Galaxy Class.
Which probably made it hugely expensive for its size. That and the fact it was really only good for war.
You would have a hell of a time, convincing another Civilization you came upon, that you where on a peaceful mission of exploration, showing up in that little death dealer.