I'm using the Defiant Refit myself and I just maxed out a few days ago. The playstyle for an escort is pretty different then either cruiser or science ship. While really advanced players probably can get Escorts to do all sorts of things, I personally have settled in on selecting a target, unloading everything and quickly getting out(or trying) of the area of engagement before the KDF collapse on me. I completely suck. However, its also a blast of a ship class to fly.