Both Marvel and DC have their old standbys. These are titles and books that will never go away. With very few exceptions, neither company will cease publishing characters like Captain America, Superman, or Spider-Man. Team books like X-Men, Avengers, or Justice League will always be published in some form.
However, every few years, the companies try to republish books that had their heyday of popularity, but never quite stuck around.
I am of course talking about your Defenders, Outsiders, New Warriors, and Suicide Squads. Books that are fondly remembered, but are not always guaranteed to be published at any given time.
The distinction is usually pretty simple. The team books that are ALWAYS published are either rock solid concepts like Justice League (all our best heroes on one team!) or a concept as distinctive as an individual character (X-Men) or somewhere in between (think Avengers, Pre-Bendis. Some headliners, but tons of characters who didn’t appear anywhere else).
The other books are ones that are usually rooted in the memory of a single creator’s run. Defenders is remembered as Marvel’s weird 70’s team book, but that’s mostly because Steve Gerber was given the reins of a random team book and went completely crazy on it. New Warriors was defined mostly by Fabian Nicenzia and Mark Bagley’s takes on what teen superheroes’ lives would be like. And John Ostrander created an incredibly rich espionage story based around super villains. The memory of these incredibly distinctive creative runs tends to do two things: generally appeal to a narrower group of fans and create a limited range of creative approaches that they will find acceptable.
An iconic mainstay, by contrast, has a much larger remit. A much broader range of stories can fit into Justice League, a book who’s description is “DC’s premier super team.” If I read a Defenders book, I probably have far more specific expectations.
Fraction’s Defenders does an admirable job of evoking the tone of the Gerber era Defenders, without feeling like a giant homage. However, you can also feel how its appeal of this sort of thing may be limited. So you can see why Marvel has tried to tinker with the concept so often. New Warriors might be the worst offender of the tinkering process. The number of different iterations that book has seen is simply staggering. New Warriors has been about everything from teen superheros to a superhero reality show to ex mutants. And none of the takes have been as successful as the original run, because that kind of creative success and timing is hard to duplicate.
That said, the one "second tier" book that manages to avoid this kind of identity problem is Thunderbolts. While it hasn’t been a huge seller in years, Thunderbolts has always stuck around and aside from a brief foray into a weird fight club comic, it never feels creatively astray. This is probably because fundamental shake ups were built into the DNA of the book by Kurt Busiek. He’s said in multiple interviews that he designed it to be completely shaken up every year or so. So as long as it involves super villains either seeking redemption or having it foisted upon them, it feels like a Thunderbolts book. Luke Cage running a suicide squad esque team out of a jail? Sure. Super villains masquerading as super heroes? Why not. Crazy super villains masquerading as people seeking redemption under the supervision of Norman Osborn? Not a problem. This approach has helped keep the book from feeling stale and it has also enabled to be well suited to adapting to new creative teams. It probably also explains why the book is still going after 15 years.
Of all the new attempts to launch new franchises in the 90’s, Thunderbolts is one of the few to stick around, and that’s probably because it’s the least tied to a single creator’s vision.