Hmmm...
When I pull up a random television network schedule from the 1970s -- let's pull up 1976-1977. (https://en.wikipedia.org/wiki/1976%E2%80%9377_United_States_...) I see some shows generally recognized as quality television.
And, er, some television that isn't. No surprise.
At least, I certainly don't think the variety shows count as "great" by most people's scope, of which 1970s television had a lot of. At least, I'm not aware of modern demand for the Tony and Dawn Rainbow Hour, Donny & Marie, the Shields and Yarnell show, or the Sonny and Cher Comedy Hour. Maybe I'm wrong.
In the scripted department, there's several single-season or less programs. I presume weren't that great. Shows like Holmes and Yo-Yo, Nashville 99, Quinn Martin's Tales of the Unexpected, and Gemini Man, were they that great? (A "TV movie" -- Riding With Death -- from the last one was used as fodder for MST3K. So, probably not.)
The one thing I think is notable in older TV listings is just how strongly several formats dominate. Namely, in addition to the variety shows, sitcoms and crime / medical dramas seem to dominate. (If you are looking for fantasy / horror / sci-fi, to give a few other genre examples, your pickings are slim.)
"Good" is by nature subjective. But one thing I can say is that none of these genres are typically noted for multilayered messaging. To give two examples from the sitcom side, here are two 1976 shows that are generally reviewed as "good": "Three's Company" and "Good Times". One is basically a farce often criticized as "jiggle television". One basically became a platform for the wacky antics of JJ. Not sure I'd describe either of these shows as very "deep". :)
Today, in the era of DVRs and on-demand streaming, I do think it's easier for writers to "risk" multi-episode plotlines.