A lot of fans approach topics like this with the mindset of a video game, where only even matches are ones worth playing.
As an avid former player of the Armada games, Bridge Commander, and Star Trek Online, that's exactly what these types of threads start to sound like. Video games are almost always different from the source material for the sake of gameplay. Let's not scoff at all the times the E-D was defeated by mighty ships; if anything, that speaks of both the strength of the enemies and the Enterprise actually surviving battles.
And above all else, yes, the ship is only as strong as the plot needs it to be -- space exploration would be boring if every new enemy ship could be defeated in a couple phaser blasts.