Gerry Conway's writing on JLA at the time (and on BATMAN and DETECTIVE) were rather juvenile and lowbrow. That was a low point for DC as a whole.
But at exactly the same time, you had Englehart/Rogers doing MISTER MIRACLE (the best post-Kirby Fourth World run of the late 1970's), as well as their collaboration on DETECTIVE COMICS 471-476, Mike Grell's run on WARLORD (particularly that first 14 issues), and several other bits of greatness, such as late-70's DC work by Starlin, O'Neil/Golden, and a few other projects that bucked the trend.
After Carmine Infantino was fired in early 1976, DC replaced him with Jeannette Kahn, whose claim to fame before taking over as head of DC was creating the juvenile-marketed DYNAMITE magazine. So clearly DC selected Kahn with the mindset of expanding younger readership.
That marketing strategy didn't really begin to diminish until Dick Giordano was hired in 1980, and an exodus of talent from Marvel (i.e., from Jim Shooter) to DC, by the likes of Starlin, Wolfman, Perez, Thomas, Colan, Moench, etc., began to revitalize DC and bring a more sophisticated storytelling approach.
On the JLA title you mention, it was interesting how despite Conway remaining on the title, JLA developed in its storytelling while Perez was penciling the book. (The JLA/JSA/New Gods storyline was in 184-185, and the rest of Perez's run was in 186, 192-197 and 200.)
I especially liked a scene with the Flash talking to the JLA in 192 playing with a Rubic's cube in his hands, and he is asked to go to a prison and check the records on a criminal. He tosses the cube in the air, and returns and catches the cube, telling the JLA all the stuff he did in a fraction of seconds!
That was pretty developed and engaging, relative to what Conway was cranking out just a few issues before.
Of the 70's post-Kirby Fourth World stories, one of the best for me was in
FIRST ISSUE SPECIAL 13 (April 1976) by O'Neil and Vosburg (out the same month that Kirby departed DC!)
Which was true to Kirby's version, and ironic in many ways, because Kirby was leaving DC over them cancelling the NEW GODS out from under him, and yet here they were publishing a new version, very true to the Kirby version, but by different hands!
I think the Fourth World books were selling well enough in 1972, and DC knew Kirby was planning to bring the Fourth World to a "Ragnarok"-like very final conclusion and kill off the characters. But DC saw these characters as very marketable, and cancelled the titles until Kirby had left DC to prevent him killing them off. And that, not low sales, was the only reason Kirby's titles were cancelled.
