Good points suss2it. Just to add to this, it seems as if relative marketing and visibility between Marvel and DC has changed since BTAS first aired. I remember a fairly well known media figure making a comment about Iron Man and the Avengers. He was saying that when he grew up evereybody knew Superman, Batman , Wonder Woman, even Aqua Man. But no one, in his circles, knew who Iron Man or any of the Avengers were. Now Iron Man, Captain America, Thor, and Nick Fury are as recognizable to kids and the public in general as are their DC counterparts.
Did Marvel's characters just recently become more interesting? Honestly, I can not answer that. In my knowledge of Marvel and DC characters, I probably have more in common with the average person in the general public than I do with some of the people on this board. My knowledge of Captain America goes back only to Brubaker, Ultimate Avengers I and II, and CA The First Avenger. My knowledge of Iron Man pre RD Jr. is scarce. While apart from general mythology, my Thor history is the same as that of Captain America and Iron Man plus a few Straczynski tales.
For a while, DC had consistent and supportive platforms for its animation: Kids WB/CW weekday afternoons plus Saturday morninngs and the Cartoon Network. Most of their animated series were getting 20-26 episode seasons for at least the first two seasons plus any additional seasons that were provided. Meanwhile, Marvel shows were all over the place and they were only getting standard 13 episode seasons. There was even a animated Spider-Man series on MTV.
Now with Disney showing Marvel animation series exclusively on Disney XD, there is a consistent platform for Marvel series to be found somewhat similar to what DC has/had with the Cartoon Network. The fact that Disney XD may be available in less homes than is the Cartoon Network does not mitigate that fact. Marvel animation now has a home, a somewhat protective environment, where its shows now have a better chance of achieving longer runs. If this was the case with Fantastic Four WGA, I would not be surprised if it would have aired for several seasons.
DC has always provided great complete season DVDs for its shows, while Marvel did not. But Marvel has noticeably improved on that front.
Plus with Disney owning Marvel, now Marvel can produce live action series for it characters, similar to what DC had on WB/CW with Smallville (10 seasons) and now Arrow.
There are a few other things that could be said, but I am trying not to be verbose. Combine all of this with some level of an attempt at correlation with the successful movie franchises, and all accompanying merchandise, and the answer to when Marvel started to pass DC becomes clearer.