In 1968 Marvel was bought by Perfect Film and Chemical and Goodman was no longer the owner. Jack Kirby left in 1970, and although his last year at Marvel was hardly inspired, it was still Kirby. According to Mark Evanier's biography of Kirby, the new owners wouldn't negotiate with Jack, nor did they try hard to keep him, which was foolish on their part of course. After Jack departed, Stan took an extended vacation and didn't write.
The new owners had a new direction for the company:
1) Initially, no more continued stories, disrupting what had been established over the last decade.
2) They wanted, instantly, a huge amount of new titles, to compete one-on-one with DC.
3) Whereas comics initially had 24 pages of art, then 20, eventually it went down to 19 with two half pages numbered separately, keeping the count at 20. DC had used half pages before, but it was a first for Marvel.
4) The prices on comics almost tripled, going from 12 cents to 35 cents in just a few years.
5) The black and white line was started.
6) They wanted to expand into the international market.
7) Under Stan, characters (except for Captain America and Nick Fury) appeared in only one comic, enabling their authors to control their continuity. Soon, most title characters had to appear in two books, with different authors, thereby complicating continuity. (Spider-Man eventually appeared in three titles.)
Stan had to adapt to changes of this kind, so how did he cope with this burden? Stan worked with Roy Thomas and created a big hit with Conan The Barbarian and later Kull The Conqueror. Marvel returned to horror with great talent in Chamber Of Darkness and Tower Of Shadows, and launched The Silver Surfer to new heights with John Buscema.
But here's the BIG thing: In 1973 Stan Lee became publisher, a fact ignored by his detractors. This was a big step up in his career, as it meant more money and prestige, with no writing or deadline pressure. He increased Marvel's overall circulation to 70,000,000. This is what businessman are paid to do, and Stan did it admirably.
By the early '70s the industry wasn't attracting many new readers and total sales were in general decline. This means that Marvel's new readers came at the expense of DC. Under Stan, Marvel's sales exceeded DC for the first time, and have remained that way ever since.
There were successes in the mid-'70s, with Stan introducing many noteworthy new comics. In 1972's America it took courage to produce Luke Cage, the first African-American hero to have his own national title. Of course, by having to produce so many new titles in so many genres, there were, inevitably, also many failures. Unlike Goodman, Stan was not the owner and had to follow instructions. With so many new titles there was no time to develop new talent, and the bookkeepers often decided which titles had to be cancelled. However, often within a failure there is success. The magazines of the mid-'70s mostly failed, but Conan, Deadly Hands Of Kung Fu and a few others were successful, though Marvel did lose most of its female readers.
Roy Thomas, in Comic Book Artist #2, 1998, talking to Stan Lee, said "There was a great drop-off in female readers in the early '70s. We came up with three strips for which you made up the names and concepts: Shanna The She-Devil, Night Nurse and The Claws Of The Cat. (We were) trying to woo the female readers back." Stan Lee said "The failure of The Cat was my biggest disappointment."
But Stan did give it the old college try.
There's no question that Lee, Kirby, and Ditko did outstanding work and nothing like that has happened since at any company. While Ditko and Kirby continued drawing and writing, Stan's career took a successful turn up the company ladder. Stan's later trajectory didn't parallel the other two - it was more perpendicular.