How long have you been reading comics? This happens ALL THE TIME. I remember when Silk was introduced in Spider-Man, not too long ago. Spider-Man was there, and around, but SILK was essentially the main focus for several issues to flesh out her story and what was going on with her. The same thing is true for Robin (Jason), Robin (Tim), the second Batgirl (Cassandra) , Signal, etc. Batman was part of the story, but many, many issues were devoted to evolve these secondary characters into the comic book universe. I remember when Amadeus Cho essentially took over the Hulk, and that was BEFORE he was the modern Hulk, but Amadeus was building his character and gathering other heroes into a team to help Hulk. I remember when Hercules TOOK OVER the Hulk comic for a couple of years! This is a very, very common thing in comics, brettc1, and you are wrong to say that Superman has never had another character "lead" the book. During the entire Kandor arc several years ago, the Kandor Nightwing and Flamebird took over Action Comics, I believe, and we often saw more of Jimmy Olsen and Lois Lane and General Lane than we did of Superman in his own title! These things happen with incredible frequency in comics, depending on the story arc, and it's a good thing - it helps develop storylines and avoid repetition.
Wonder Woman is one of my favorite titles and characters, and has been since Polly was retroactively introduced to have been the Golden Age Wonder Woman (so many years ago), but Robinson spoke truth to power when he spoke about a big part of her fanbase that seems to always know what is best and is hypercritical of writers, especially male writers. It's rather unfortunate, because it gets in the way of potentially interesting and diverse storylines and potential. I've always found that Wonder Woman is a great title for strong female secondary characters, but Steve has really been the single male supportive character (unless it was another potential love interest). Superman has Lana, Lois, Kara, Martha, as well as Pete, Jimmy, Jonathan, etc. So, you would think that the balance of male and female characters would be more equal in Wonder Woman, but it never has been. Why do you think that is? I think this whole Jason storyline and the "rabid fan base" response shows EXACTLY why that is. If you introduce a male supporting character in Wonder Woman and give him the equal amount of time that Lana or Lois might get in Superman, the alleged "rabid" Wonder Woman fanbase gets angry. I understand that they don't want the strongest DC female superhero character to lose "airtime" or get overshadowed, but that consistent response, over and over, writer to writer, leads to a serious potential for problems in interesting storylines for DC. It shouldn't have to be that way.
Perhaps the answer should be that that Wonder Woman be given TWO titles. I mean, Superman has both Superman and Action Comics, and Batman has both Detective Comics and Batman, so why shouldn't Wonder Woman have two ongoing titles -- one devoted to Wonder Woman always being front and center and never sharing the limelight with any other potential major character, to appease one group, and one devoted to a more balanced cast of characters made up of both women and men, like you frequently see in the Batman and Superman franchise, with WW still being the lead usually in her own book. My guess that would relieve a lot of these weird dynamics, and I'd be 100% supportive of both titles myself!
Now, I didn't like Jason as a PERSON much, but I'm not sure we were supposed to. He's no Lana Lang, Kara, or Lois Lane - he's a screw up, easily manipulated and gullible, but with a good heart in the end. So, I NEVER THOUGHT HE WAS TAKING AWAY THE SPOTLIGHT AS THE HERO OF THE BOOK. That actually impressed me - Robinson was trying to walk a tightrope given to him by Geoff Johns -- introduce a new MALE character to the Wonder Woman universe, give him powers, but don't have him eclipse Diana - let her be the hero he looks up to. I think Robinson did exactly that. The vest is interesting - it was meant for Diana and it would have made her clearly more powerful than Superman if she had it, and I still wonder if she may use it someday if a writer decides to go that way. However, for now, it gives Jason at least a fighting chance to survive life with the Dark Gods. It also leads to a potential storyline where Jason "grows up" and becomes a hero largely on his own, fighting them or at least guiding them to their universe. Maybe he really does become more of a "Jason and the Argonauts" like character as a result of that experience! Maybe he becomes a Knight-Errant who goes throughout the universe, helping people whenever they need it, but often getting sidetracked because of this need to help people coupled with (what seems to be) ADHD - easily distracted from his goals. In any case, at least having the "God Vest" helps him on that journey.
Again, I may not like Jason that much, even now, as a character - but I think Robinson did a good job of giving him some dimensions without overshadowing Diana for the issues he was in the cast. I'm sorry some folks don't agree with that assessment, but I doubt those folks would have appreciated a stronger, more assertive, more confident twin brother character, had Robinson gone that direction either.
By the way, one last point with respect to Jason "saving the day" in issue 50. That is the way it should have been, since he was "going away" after this storyline and according to the prophecy from Geoff Johns' storyline, Jason was destined to "save the day." So, Robinson did EXACTLY what he set out to do - bring that storyline to a place where the "prophecy" could be fulfilled. Did Diana do much? No. But, again, I've read many comics in which Spider-Man, Hulk, Superman, Batman, Iron Man, and other male characters have had another, secondary character, make the "sacrifice" to end the storyline, often while the hero is yelling "NOOOOOO!" Jane Foster is probably a bad example, since she WAS the main character in Thor for awhile, but she's the most obvious recent character to do that and it was Odinson who was screaming "NOOOOO!" I remember tons of secondary characters actually making the ULTIMATE sacrifice in many plotlines over the years to save the day - and one could argue sometimes that is why they exist, to sacrifice for the life and safety of the hero of the book. Perhaps the best example is Bucky Barnes - who in Marvel cannon was dead for 50 + years, before he was returned as Winter Soldier. Who can forget Captain America screaming at Bucky to "LET GO, LET GO!!!!"? In a kinda, sorta way, Jason is to Diana as Bucky was to Captain America.