One of the more recent additions to the Star Trek Universe is that of the Federation warship. Starfleet had long deemed the dedicated warship to be unnecessary, especially as its exploratory starships had been more than a match for the purpose-built, but technologically inferior, Klingon and Romulan warships for well over a century. The most notable example of this disparity was when the impending arrival of six Federation starships (a Galaxy, two Excelsiors, and three Mirandas) forced a Klingon fleet of 200 warships (of all four main types) to stop attacking Deep Space 9 and retreat ("Way of the Warrior Part 2" [DS9])...and Klingons are not known for cowardice in battle (indeed, they relish fights where the odds are against them). Klingon captains will attack, without hesitation, enemy ships that outgun their own 10:1, even if their own vessel is severely damaged.
What changed Starfleet's apathy towards warships was the Enterprise-D's encounter with the Borg Collective in 2365. The discovery of such a powerful, and implacable, enemy forced Starfleet to start building ships that had previously been limited to concept studies. These ships possessed tactical capabilities that were grossly in excess of what was needed to defend the Federation against Alpha-Quadrant threats - but adequate (so far) to protect the Federation from extraquadrant threats such as the Dominion and the Borg.
Note 1: In regards to the Defiant's performance against the Borg in "Star Trek: First Contact" versus then-Commander Sisko's statement nearly 3 years earlier that the ship "...was designed for one purpose only: to fight and defeat the Borg" ("The Search Part 1", [DS9]), it should be kept in mind that the Defiant, whose design was begun in 2366, would have been expected to combat Borg Cubes similar to the 250-billion ton old-style models encountered in "Q Who?" [TNG] and "The Best of Both Worlds" [TNG]. It was not the fault of its designers that the Defiant was sent against a Borg Cube ten times as large and powerful as its anticipated opponent (though this would explain why the Defiant project was abandoned in favor of the Sovereign as Starfleet's anti-Borg starship after Picard's recovery from the Borg collective - as Locutus, Picard would have learned that the Borg had the ability to build a Cube much more powerful than the one encountered in "Q Who?", and would have warned Starfleet accordingly after his deassimilation).
Note 2: Of course, it must be noted that any starship, no matter how powerful, can be overcome by vastly inferior forces due to bad luck, unfamiliar weapons technology ("The Jem'Hadar" [DS9]), or a plot-mandated loss of crew competence - one notorious example of the last being the defeat, boarding, and capture of the USS Enterprise-D by a pair of surplus Klingon Bird-of-Preys collectively crewed by a few dozen renegade Ferengi. ("Rascals" [TNG])
Note: Yes, I am aware that the registry number on the hull of the Prometheus was NX-59650. However, the dedication plaque and the ship status board used the designation NX-74913, which is much more in line with a vessel as recent as the Prometheus was.