Personally, I find Roddenberry's vision to be rather suspect and unflattering at times, and while I would never want
Star Trek to discard its roots or stray from the fundamentals of what makes the franchise so inspiring, I think Trek is much improved by having those involved in its creation pull in directions that Roddenberry would resist. Never to defeat Roddenberry, of course, but to exist in symbiosis with him, to generate enough friction and conflict that interesting stories can arise from it. Trek is about exploration, yes, outer and inner? Roddenberry should be the homeworld, but we need to escape that world's gravity well and go exploring, even if we never lose sight of its status as our emotional core. So long as we have home in the back of our minds and cruise back there periodically to recharge and refuel, we can't let ourselves be tied to it. Faith of the heart, and all that.
To point out the obvious, large-scale wars can drag out for some years, and the Dominion conflict was set up as a large-scale problem - the war arc wasn't war for the sake of war, it was an extension of the political story arcs that had been unfolding successfully for some time. I prefer having the Dominion War take place over the entirety of the final two seasons rather than being swiftly resolved as though it were a minor distraction or a cheap detour. War has a massive impact on people and cultures in so many ways, particularly when it comes to define an era, and having it as a backdrop throughout the two seasons, even when it wasn't being focused on, was fantastic in my opinion. Plus, it's not like the Federation wanted a war or suddenly became warlike. It was shown to be in a position where it decided it had to fight one if it didn't want the Dominion to annex the Alpha and Beta quadrants. And that was the catalyst for a lot of examination of the Federation, Klingons, Cardassians, and others, where they had found themselves and where they might be headed. That sort of reflection and probing examination seems more in keeping with the idea of a provocative science fiction franchise than adherence to a creative dogma. There was a lot of great story-telling stemming from the Dominion War arc; it wasn't a flashy focus on battles or explosions, which is the only thing I'd really take exception to. There didn't need to be a war, but there didn't need to not be a war either.
Wars should be used sparingly in Trek, but if there's justifiable reason for them, make the most of it the way you would any story.