but it does matter-it changes the argument. The argument is about weakening an otherwise powerful enemy through over-use when they're defeated every time they are faced. You can't weaken an enemy through over-use if they're only used once.
Of course it weakens the enemy even if they're only used once, defeating them even once weakens them and shows they weren't so tough and the main characters shouldn't have been so scared of them in the first place.
Q showed up repeatedly, no one ever says he lost his menace.
but it doesn't matter if you weaken a one-shot adversary by the end of the episode, because you're not bringing them back as supposedly intimidating adversaries for another episode later.
Q was never really "defeated" in his appearances, so that doesn't really apply. Also, he became more of a comedy character than a villain.
Yeah, it does matter. Because by defeating/destroying them you still weaken them. It doesn't matter if they show up again.
Q made repeated appearances, and no one ever claimed he was "decayed" as a villain.
Hell, Voyager does the reasonable thing and shows that the Borg were not the ultimate species of this Galaxy (which we already knew) by showing other aliens more powerful than them.
What reaction does the show get? That by showing that there was someone more powerful than the Borg (despite ALREADY KNOWING THAT) the Borg have been weakened.
It's moronic, it truly is.
The worst part is, if TNG had introduced the 8472 aliens NO ONE would complain that there were other aliens more powerful than the Borg.