2. It's A Rush Job
It sounds silly to say that the Justice League movie feels rushed given that the script has been in various stages of production for about a decade, but there's a pronounced feeling that Warner were keeping their eye on The Avengers to see how well it performed. After its astronomical box office success (becoming easily the highest-grossing film of 2012), Warner decided to push ahead with a Justice League film to try and capitalise on a similar type of success, while seemingly failing to remember that Marvel had spent years developing the various characters in their own movies. Warner needs to slow down and appreciate that trying to keep up with Marvel will be their end; Marvel has a strong, popular framework from which to operate, and the DCU does not have that yet. Warner needs to ensure that they work at their own pace and forget about Marvel; trying to compete with almost surely see them flop at this stage.