While I agree TNG was more “stuffy” the examples you’d described were no different to the lighter elements in TNG. Eg most of the sub-plots that involved either Data were like that. Most of the Q episodes too. There was plenty of banter on TNG, what DS9 did differently was showed people being snarky with each other. Every episode of DS9 had someone delivering a cutting putdown to a colleague. This was something TNG lacked (because Gene Roddenberry didn’t think it worked with his vision but he was dead by the time DS9 was being written).
> A lot of what I said about DS9 applies to Babylon 5 as well.
B5 was originally pitched to the same network as Star Trek (Paramount?) but was rejected. Then a few months later DS9 was being produced. Straczynski (the creator of B5) had accused DS9 of ripping off his ideas. And to be fair there are parallels to his show: darker plot with a story arc about impending war based on a space station that hosts an array of aliens who don’t all get along. Even the worm hole idea could be related to the jump gates in B5 - both are subspace portals created by ancient aliens.
But you can also see a lot of parallels between SG1 and B5/DS9 too so it’s fair to say all art inspires other art.
I do miss 90s SciFi too and agree with your points about how dark things have gotten these days.