I don't wanna piss on anyone's parade, but I'm okay with how it all played out in TOS movies. Couple of reasons...
Star Trek isn't about space battles, so we needn't have every movie featuring ships blasting other ships (although that's what we generally get).
Sure, the Enterprise is armed, but combat isn't the main purpose of the vessel, merely one part of a larger mission. Starships are supposed to be about exploring strange new worlds, going where no man has gone before. Kirk's prologue didn't mention defending Federation against any and all attackers. As for me, TMP was really all about what a starship can do... exploring the unknown, saving a planet, new discoveries. That's more "starship" to me rather than how much whoop-ass it dishes out onscreen. TMP showed a starship succeeding in a high-risk mission without firing a shot in anger. That's Star Trek.
The movies weren't about all-out warfighting, so we did not get a grandly matched battle of "our best" versus "their best". The Enterprise fought diverse vessels under varying circumstances as the plot unfolded. Sometimes a commandeered friendly ship, sometimes a lesser enemy combatant, whatever it may be. More interesting that way.
Lest I be misunderstood, I enjoy seeing the Enterprise kick ass, too. But that's the gravy on top, I'm more impressed when I can see the starship Enterprise do other great things, acting in a benevolent manner for all mankind, or other high sounding words.
There are plenty of kick-ass fighting spaceships around. Let the starship Enterprise be something more.