I have a feeling this might be no small part in why TOS and TNG are the two ST series that contain 90% of the "only comes up once" sci-fi plots / concepts / worldbuilding that people ever make reference to when talking about "things from Star Trek" rather than when talking about Star Trek. TOS and TNG, while definitely soft sci-fi, were to some degree trying to create 22-minute-long works of literary Speculative Fiction, modelled after the sort of things you'd read in serial SF magazines of the 1950s. Later ST series are emphatically not that, and nor do they try to be.
But as you said, I think it ends up with a higher quality show.
An annoying facet of ST episodes is the morality lessons they push, like on every episode of The Brady Bunch.
It’s nice to watch something that highlights the best of humanity in a future setting.
Almost everything else in SciFi is dystopian. But ST is a rarity. And it’s all the more beautiful for it.
The difference was that rather than turn it into soap opera porn, the characters actually tried to behave professionally (most of the time).
• DS9 only had a little soap-opera drama, serving as almost a kind of fanservice sprinkled judiciously into otherwise-thematic B-plots.
• VOY had more, with entire B-plots of episodes now being character-focused, including a few arcs that would have worked just as well if transplanted into some modern-age military drama with no SF elements.
• Drama-as-the-A-plot episodes were appearing by ENT.
(After that I stopped watching, but I've heard the trend has just continued from there.)
But when you only have half a dozen-ish episodes per season, you can't afford filler.
I really enjoyed TNG as well, and DS9 probably wouldn't have even happened if not for TNG's excellence. I never really felt like the writers gave Picard's character a lot of room to change, though. A lot of the time, he was almost like the sitcom dad who was mainly there to teach the kids a lesson at the end of the episode. That's not a knock on Stewart's acting ability; I'd say he was almost certainly the best actor on the show.
Also agree about Bashir.
And some of O'Brien‘s best performances were counterpointing Bashir too.
I think as a solo character, he’s a little shallow. But he works exceptionally well at being an anchor for other characters to play off.
But yes, those instances were a bit rare.