Marvel eased audiences into their format, I think that's something the WB execs fail to realize. I'm not talking about requiring set up movies for every character either. Something like Civil War would have been impossible to digest in phase 1. It would have been rejected completely. The world building Marvel did in phase 1 was subtle enough to make each movie feel like it's working independently in a bigger world rather than cramming this huge universe into the forefront like they've done with the DCEU.
Think about "Fury's Big Week" as a concept. Incredible Hulk, Iron Man 2, Thor, and the recovery of Captain America all occur in the same week with much of the timeline overlapping. That might sound like they were trying to put the focus on the cinematic universe rather than the character stories but Fury's Big Week is something that happens in the background. It's not the focus at all! Instead, they used the timing of events to isolate each movie and then had Coulson and Fury peppered throughout to interlock the universe. That way, people who were paying attention felt like they were getting an extra pay-off while people who weren't didn't even notice the Easter eggs tying the universe together. And then of course Avengers came in and really sold the whole cinematic universe concept. Sequel bait didn't really become a problem until Age of Ultron, and much of that was a product of studio meddling as well.
It felt like DC was going to do something similar after MoS but then they just dove in head on in BvS without really thinking about how teasers should work in the context of stand alone films. Apocalypse also had this problem with how they overtly used Phoenix in a movie that wasn't about the Phoenix Force to begin with. Contrast that with X2 where Jean's death hints at something more for the fans but doesn't bonk you over the head with "THIS IS IMPORTANT. THIS WILL BE IN FUTURE MOVIES." Marvel has only done this twice, really, with AoU and Civil War. The latter only gets away with it because it's a better movie and also because it wasn't as clumsy as AoU with its hot tub Thor machine.