If TNG had introduced the 8472 aliens, would you still say that? Or what if they had shown Q casually destroying a Borg ship?
Yes I would have, because 8472 were poorly executed.
As for Q destroying a borg ship, well he's practically a god, so it wouldn't be as big a blow, and if TNG had done it, it would have been well written, and served to make Q look even more powerful and menacing, while not harming the borg that much, because of how powerful Q is (above ALL others).
In voyager we got Q in a bath kissing janeways foot, just as we had him getting floored by sisko in DS9.
That's the problem, TNG knew how to keep characters and species sacred, Q, The Borg, Lore.
Granted, there were some comedic moments, but they let it be known, these guys are Dangerous, in a way Voyager never could manage.