The greatest issues facing the DC Comics movies are three-fold.
Warner Bros. Executives
The first problem is not unique to the DC Comics movies. Many movies have suffered because of the interference of studio-executives, such as The Amazing Spider-Man 2, F4ntastic, and X-Men Origins. Many studio executives are older, making them risk-adverse, and closed-off to content that is unfamiliar to them. Worse yet, many of these studio executives are obsequious in their pandering to shareholders. If a project doesn't seem like it will have mass appeal, or some easily marketable angle, then it will be hell to get said project greenlit, and even more hellish to keep the initial vision intact. It is public knowledge that the DCEU has suffered heavily from studio-intereference, especially when it comes to Batman v Superman, and Suicide Squad. If Warner Bros. executives don't learn to keep their distance, then we can expect future DCEU films to struggle to convey the intended vision as have BvM, and Suicide Squad.
A Lack of Confidence in Their Own Vision
The second problem is that Warner Bros. is too worried about critical consensus. The reaction from fans and the general audience has largely been favorable, in terms of reviews and revenue. Although no DCEU film has outgrossed an Avengers film, every DCEU film thus far has managed to outgross the bulk of Marvel's movies. Rather than take that fact in stride, and push forward, Warner Bros. opts to remain disappointed that their films habe yet to earn $1 billion (as if anything less than that figure is somehow unprofitable). While Warner Bros. is busy fretting over what the critics have to say, Universal churns out a "Bayformers" movie every couple of years and laughs all the way to the bank as critics moan about the "tragedy of it all." Warner Bros. needs to simply make the films that they set out to make instead of reacting to every bit of unfavorable press. Warner Bros. takes ever negative comment as the gospel, making them quick to reshoot, rewrite, or scrap film ideas to appease people thst aren't necessarily seeking to be pleased.
Thinking that a DCEU is Necessary to Begin With
Even though Marvel gets most of the shine, the fact of the matter is that Warner Bros. has been putting out superhero and comicbook films for the past 38 years. While there have been a few duds, most of their films have done pretty well in terms of box office revenue (Superman, Batman, Constantine, V for Vendetta, A History of Violence, Red, 300, The Dark Knight trilogy). DC could have simply made an excellent trilogy out of Man of Steel and moved on to something else (such as rebooting Green Lantern).
There was never any real need for Warner Bros. to make a shared cinematic universe as much as there was a need for them to simply put out a greater number of comicbook films that didn't involve Batman or Superman, and do so on a more frequent basis. And rather than worry about whether or not their films are grossing $1 billion, they should have simply focused on the profitability of the project. V for Vendetta didn't even gross $200 million, but was still a success (it earned $132 million against a budget of $54 million).
Hellboy, Kick-Ass, and many other films have proven that there is plenty of money to go around in the genre without having to copy or compete directly with Marvel. Warner Bros. has the distinct advantage of having the rights to all of the DC Comics characters. Warner Bros. should be plying that advantage to put out more diverse content than Marvel.
