I think the starships were subject to the demands of plot. The Voyager
, one of the Federation's newest ships built to specifications acquired from battling the Borg, was consistently bested in combat by less advanced ships in the Delta Quadrant.
I don't have an issue with the older classes being used in the Dominion War. I do have an issue with them being used in the front line. And, I do have issues with Starfleet having to kitbash ships.