I get the appeal. Cross overs are enticing. But Zach Snyder’s justice League demonstrates a huge challenge that most people don’t seem to discuss: the recruitment needs to have a purpose.
Remember when Batman is asking Aquaman to be in his movie team? It’s clear that the only reason is that the team is not a means, it’s the end. He doesn’t need him for any particular reason, he just spends the he could be trying to solve a mystery building a club from scratch with no clear purpose. I think this set up would have the same problem.