And then Marvel systematically screwed the artists out of credit, residuals, and just in general. They're still doing this, too. DC's not much better, either.
Pardon the slight rantiness here. I'm an artist so the creative credit going to the party who does the LEAST amount of the creative work bugs me.
Various writer-editors were given the title of editor-in-chief but they really didn't do that job. Roy Thomas, Len Wein, Wolfman, Gerry Conway (for less than 2 months), and then Archie Goodwin all had a significant amount of reprinted comics published because the new issues weren't done in time. Readers hate reprinted stories. (The only writer-editor who did not become editor-in-chief was Steve Gerber.)
What stopped this trend? Marvel hired an editor to be an editor-in-chief. This annoyed a few of the writer-editors and so most left in dramatic diva fashion.
Most comic fans do consider the 60's Marvel as equally good as the 80's Marvel, which includes Walter Simonson's Thor, Frank Miller's Daredevil, Byrne's Fantastic Four, Roger Stern and John Romita Jr's Amazing Spider-Man, and Claremont, et al's X-Men.
70's DC is an example of how to ruin a company. Without detailing their editorial problems, let's focus on two significant events. Sometime during 1972 and 1974, Marvel starts to outside DC for the first time in history. Except for a handful of months, this has been true until very recently. The second event is known as the DC implosion. DC screwed up and had to cancel a large number of their titles. Much of their talent landed jobs at Marvel.
So Wolfman and the other writer-editors jumping ship for DC was not a step up. It was a step away from meeting deadlines, and other responsibilities. Lee understood that no editor-in-chief could edit the writer-editors, which is likely why he left when he did.
Consider the case of comics, particularly Marvel and DC. I'm a huge fan of Stan Lee's work from the 1960's and 1970's and I like some Marvel and DC stuff after that.
Lee created some incredibly popular characters in the "Silver Age" but nothing added later really caught on. But, 40 years on, what can you write about the Incredible Hulk? How many times can Magneto trash the X-Men's house?
Sure, later on the comic houses published some books by Frank Miller and others that had more literary and artistic pretention, but none of those sold as well.
By 2000 or so both Marvel and DC flirted with bankruptcy and got bought by media conglomerates because movies about comic book characters were much more profitable than comic books.