It would vary quite a bit between who were the writers or artists and the circumstances.When Lee was writing 6 or 7 books a month and Kirby was the artist,I'd think Stan only provided one or 2 sentences of plot.Same with Ditko.Sometimes those 2 did the plotting themselves.But with Colan,Romita and Heck more initial plotting was done upfront. In the case you saw,its hard to judge since you didn't see what Roy originally provided,how much was Steranko repeating back or fine-tuning. But I do think Steranko fell into the Kirby/Ditko class as well as Neal Adams

Wasn't Steranko one of the few artists to whom Marvel actually gave a writing credit to?

Kirby admired Steranko, but I think, given all that the King gave to Marvel, it miffed him a bit that he wasn't granted the same.

I think when it was just Lee and/or Thomas "writing" everything, the artists were the real creative control on the books, developing the concepts, characters, and plots. As marvel moved in to the 70s, writers such as Moench and Claremont were much moe active in developing the plots and concepts and artists took more and more the back seat on those matters.

There are creators who still use the Marvel method or at least a somewhat modified version these days. Matt Wagner, for example, likes to give a fairly detailed plot, waits to recieve the art, then does the dialogue as he often finds that his artist finds some element in the plot that he hadn't concieved of when they visualized the story. Walt Simonson also likes to work Marvel style when he's writing a story for an artist. Both of those gentlemen are legendary artists in their own right, and they know what an artist can bring to a story with guidance that permits some interpretation.

One thing I'm learning as I read more articles, books, listen to podcasts, etc., in regards to classic creators, is that many older artists who started in the Golden Age didn't necessarily care about the characters or stories all that much; they were mainly passionate about the artwork and the storytelling as it related to the artwork.(Sort of a method over concept kind of thing.) I think this is still hard for some fans to wrap their heads around. It was for me when I was younger.

when did the marvel method end and why?

i always think that alan moore's very very detailed scripts and maybe just him as a person and how he worked with artists, often got those artists to produce some of their finest art which seems counter intuitive - being so prescriptive should stifle the artist. (he said vaguely)

If I had to guess I would say it ended at Marvel when the Quesada era started (mid-to-late 90's-early 2000s) and writers like Bendis came to the fore who were writing for the six issue arc and controlling the pacing to do so. Writers who approached the story telling from a visual point of view and wanted to have more say in the visuals as well as the text of the story. It was an influx of writers almost a new generation who were influenced by things like Robert McKee's screenwriting book/seminar story, and the David Mamet book on directing (both of which Bendis brought up every time he talked about his influences). It was the post-image era, when the flash of the Image art first approach had fizzled and the idea of super-star writers was emerging. Writers were being recruited from other mediums and people were looking at the possibilities of the medium of comics, but the focus shifted to the writers and so more control of the project was ceded to them. Neil Gaiman, Warren Ellis, Garth Ennis, Kurt Busiek, Mark Waid, etc. etc. became he creative superstars and the full script re-asserted itself as the norm. Those writers form other mediums (Kevin Smith, Brad Meltzer, etc.) were used to the full script and even screenplay/teleplay formats and used them as well. What was different though, was that almost to a person, those writers talked about tailoring the scripts to the strengths of the artists, of knowing who they were working with and of having a lot of back and forths with the artists throughout the creative process. In the old days it required being in the bullpen to be able to do this, or working on site, but with advances in communication tech in the 90's, especially the growth of the net and the ability to share files and instantly communicate no matter what the distance, allowed for a more collaborative approach but still having the full script be the framework, allowing the artists to have input without necessarily going full on Marvel method. 

Again this is only a guess on my part based on interviews and back page matter I have read and such. 

-M