It’s weird that for so long the prestige, “prime time” model of TV was basically character types in disconnected but formulaic vignette plots and “multi-episode plot arcs driven by changing character dynamics as plotted by a coherent creative team” was the degraded, low-status daytime “soap” form

People date the “Golden Age of TV” to The Sopranos but I think the key was reversing this and that started in the decade prior. By the time it debuted in 1999, Buffy the Vampire Slayer and Xena: Warrior Princess already had a real reputation for that (and for playful writing with self- and genre-awareness, which was impressive when you consider they were both based around fight scenes); the X-Files was famous for balancing monster-of-the-week and broader series mythology.

You can see the progression in the Star Trek serieses - TOS was barely consistent from episode to episode; TNG had the Borg arc and recurring Q episodes but also the entirely abandoned Season 1 arc about corruption and betrayal in Starfleet; by DS9 they kicked off the series by plopping the station next to a blob of long-term plot and introducing elements – Sisko as Emissary of the Prophets – that didn’t resolve for seasons.

Maybe further back to the 80s, when this even became possible as shows staffed up their writers’ rooms enough to produce consistent work in-house rather than just taking freelance pitches and polishing them. Miami Vice was a breakthrough not just for the cinematic style and contemporary pop score but that it had elements of overarching plot – the hunt for Calderone, Sonny’s amnesia (how soapy!) – at all