It shouldn't have been that hard. Now they're back to square one when they could have been reaping the benefits of a BvS/JL crossover right now had they done their due diligence
2013 - Man of Steel
2016 - Wonder Woman, The Batman -------- Get solo films out for the trinity first before even attempting a crossover, because so much of what was done in BvS was an attempt to build for future movies. Now, you already have some character development in place you can build off of instead of trying to synthesize it all in one movie
2017 - Man of Steel II, The Flash -------- You needed a MoS 2 out as well because MoS 1 failed in many regards in getting us to care about the Cavill Superman. BvS would have needed to correct the Superman character in addition to living up to all the expectations, you shift some of that legwork to a sequel solo that gets the character and audience ready for BvS. Throw in a Flash movie the same year because it's easy to sell and will help you out down the line for JL
2018 - Batman v Superman, Suicide Squad -------- Now you can do your big blockbuster crossover movie and have a solid foundation to do so. They tried to half-ass in a "post-Superman world" which didn't work for several reasons, so save the actual Death of Superman storyline for when the time is right, which would be way down the line, and when the audience is truly invested in the Superman character. Similar to how Avengers 1 was a launching pad for all the movies that came after, you'd do the same with BvS. Have Suicide Squad be a welcome summer reprieve from all the "god" characters.
Then you can build to your Justice League movie and do WW2, Aquaman, Shazam, GL Corps, Cyborg, Birds of Prey, etc.
