TNG was made to be completely episodic, the characters weren't meant to develop. They were fully formed at the start of the show, same till the end. It's only till the movies do they get some YMMV(Dune buggy) development. Picard goes through some serious **** yet is completely fine the next episode. Four lights, living a lifetime in a day, locutus. Data never used the emotion chip because that would outright break the episodic format.
They do have some casually linked episodes like Data's/Lore/origin arc which being an emotionless android means he doesn't change, Leah Barhams doesn't stay on the ship, Moriarty gets trapped in a cube universe, Barclay doesn't appear often enough to matter getting more development in Voyager. Picard, Riker, Troi, Crusher, Worf doesn't change one bit. They reset every time. As much as Voyager is a the known reset button show mostly by ignoring it's premise, it's has far more serialisation.
TNG's writing is perfectly fine. Your misunderstanding of what the show is and the 90's TV production ethos is throwing you off target. Shows then aimmed for syndication. To do this TNG is a procedural, monster appears, spacehole, holodeck does weird thing, alien possession in a self contained episodes with static characters are much easier to write can produce an arbitrary number of episodes.
Soft/Serialised shows like Babylon 5, Stargate/DS9 format were the exceptions. Prestige TV wasn't really a concept, they made for TV miniseries, direct to video which are movies of sorts made on a TV budget.
UK/AUS/NZ and Animé are different favouring much shorter, planned out shows or the other extreme which shows that go one forever which are much rarer in American productions due to different budgeting structure. Coronation street, Doctor Who, Neighbours, Shortland street, Conan. The vast majority of Animé is serialised. In Coronation street you could be on the show until you died irl decades later.