I could be wrong but I think the far bigger difference from then to today is not the quality of the journalism out of mainstream outlets but that the plethora of outlets available has removed the necessity of consensus myth making. Instead of a collected national myth that Americans share they can now choose their own myth.
They used to have to bend their views somewhat towards the major news because people seek to resolve their cognitive dissonance. Now they can change the channel. As an example, my parents are conservative and when Walter Cronkite criticized the Vietnam War and journalists put direct images of the conflict on TV they praised that. Yet when mainstream news which had generally backed the war in Iraq began to report on things going wrong there my parents were livid. When news outlets began reporting on soldiers dying and reading the names of the dead they were even angrier. Nevermind that the news was unable to air the kinds of direct footage of war they had in the 60s because the military had become much savier about the kinds of situations they let reporters into.
I think major news had almost the exact same, pro establishment, upper middle class ivy league bias it has today. I just think it's easier to confirm a contrary opinion. If Fox News existed in the sixties I think it would've run with slander stories about MLK for example and might've hampered Civil Rights. But they didn't exist and general regard for MLK as a hero became the default myth.
Again, I could be wrong but I think it's a perspective worth putting up against the common narrative.
And it seems to have become acceptable (on both left and right) for a news room to try to "get" a sitting President that they don't like, even if the result is sloppy journalism.
My impressions is that serious retractions (or worse, serious errors without retractions) are far more common now than thirty years ago.
As for MLK, even knowing what we do now, I still consider him a hero. But yeah, journalistic coverage of him back then was pretty uncritical.