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.