TNG created new villans/aliens.The Ferengi (for a time), Q and The Borg, they did not rehash dangers from the past e.g The Tholian Web, The Apollo God,
For half the run of DS9, the main antagonists were a rehash of a TNG alien.

What's important isn't "have we seen it before", it's "is the way we are seeing it now good". "Original" and "good" aren't even correlated with one another, they're two completely unrelated concepts and neither so much as implies the other. I mean, yes the TNG introduced Ferengi. But the Ferengi were horrible, annoying, gamboling goblins in TNG with nothing interesting to them whatsoever. Being original didn't make them any good; they weren't any good until DS9 took the race (instead of coming up with a new one) and did interesting things with them.