The debate has now been should DC/Warners follow the footprint that Marvel established, and is proven by Marvel to work if done right, or should they forge their own path. Well, the reason Marvel's strategy worked was that they produced successful solo films with the characters (to varying degrees of success, to be sure) and then once those characters were set up, brought them together into a major action blockbuster. So fans of each individual film wanted to see what could possibly bring together all those characters.
Now here is my thought on the mistake of not following that model... If you do another Superman film with additional hints of other heroes and maybe one guest appearance by one of those heroes, and then jump into a Justice League film... You have to spend a part of that JL film setting up the other heroes. AND... Should the Justice League film fail, those potential solo projects are dead in the water. BUT... if you do the solo films first and do them right, and they are at least moderately successful, then you can bring the heroes together and hope that the JL film would be also successful.
Unfortunately DC/Warners is in the unenviable position of being "damned if you do, damned if you don't". Since Marvel did it first, if DC/Warners follows Marvel's model with solo films leading to a JL film, they will be perceived as copying Marvel. That will hang over DCs head through the whole process. It is unavoidable so any success of the films will be partly tainted in the public eye by the perception that DC is copying Marvel. This will be true regardless of the level of success of the fims following the Marvel model.
If on the other hand DC/Warners does another Superman and then right into Justice League, and it fails... the perception will be "Why didn't they do it the way Marvel did?". IMO they will have a hard time achieving JL success without the buildup, so it is less likely they will succeed if they forge their own path, but I may be mistaken. It depends... but the Green Lantern of JL will confuse some if they intend to reboot Green Lantern, since it won't be the Ryan Reynolds version.
In the end, DC/Warners needs to take their time and consider all of this in their decision making process and make decisions based on careful consideration of story and not make the decisions solely based on being similar or different from Marvel. If the base of their decision is due to what Marvel has done... they may be doomed to failure before they start. IMHO.