In one form or another, there has always been something of a battle between Marvel and DC. You can't have two companies working in the same industry and appealing to the same customers without some sort of conflict arising. Having said that, there is ultimately plenty of business to go around, and since everybody who loves Marvel or DC just loves good superhero stories, a win for one company is really a win for both. This is especially clear when one learns that when Kevin Feige discovered James Gunn was going to make The Suicide Squad, the Marvel Studios chief just wanted to see Gunn make a good movie.
James Gunn's career in the last year and a half has had ups and downs on par with Guardians of the Galaxy - Mission: Breakout at Disneyland Resort. First, he was moving forward on Guardians of the Galaxy Vol. 3, then he was fired from the film. Then he was hired by Warner Bros. to make a sequel to the hit Suicide Squad, and then, literally the next day, Gunn and Marvel came to terms to bring him back. James Gunn tells Empire that when he informed Marvel Studios' head Kevin Feige that he had agreed to make a movie for DC, Feige only had one comment...
Please, please make a good movie. Just… make a great movie.
Kevin Feige could have been frustrated or annoyed that James Gunn was going to work for "the other guys," but instead, he just wanted to see a good movie. And in the end, that's the case for all of us, right? You might have a particular love for Marvel Comics or the MCU, but if you like superhero stories in general, then you're going to want every one of them to be good, even the ones made by "the competition." And Kevin Feige is working at Marvel Studios now in part because he's as much a fan of superheroes as anybody.
It seems quite likely that Kevin Feige is truly supporting DC's movies, because, as it turns out, if Feige really wanted to torpedo The Suicide Squad, he could do it. James Gunn tells Empire that Feige was very aware of the upcoming film's roster before it was officially announced, and Feige is currently privy to some information that has yet to be publicly released...
Kevin knew who all those characters were for months before we revealed them at FanDome. He still knows who the villain is. I think he’s pretty trustworthy with his NDA!
There could be some very suspicious leaks revealing secret information that DC doesn't want out there, but that hasn't happened. The fact is that comic book movie success from one company benefits the other, and generally speaking, most fans aren't forced to choose between which movies they see, so everybody wins.