Part of the reason why TNG was good beyond the first couple seasons was because of the open script submission policy that’s no longer in existence. According to ex-Trek producer Ronald D. Moore, they were reading something like 3000 scripts a year. It allowed them to be choosy (though there were still some stinkers). Now that the characters are established, if the seasons were longer, it might be cool to see the open script submissions come back (though, as I’m typing this, maybe implementing this during or shortly after a writers strike would be a poor choice, even though there were limits to how many scripts one could submit before going through “official” channels). Anyway, one could argue that a huge amount of ideas need to be generated for a show as great as TNG to exist, more than a small group of writers could produce. If outside script admissions were allowed, I’m sure we’d see some great sci-fi episodes from writers who weren’t even thinking “Star Trek” as they wrote them.
I’m not against filler, and my post may have come off as being that way. Not every story has to advance character or advance some storyline. I’m just against bad filler.