One nice thing about LoS is the full roster. They have a hero for everything. But when I think about how they built the team (large benefactor, recruit), there is the potential for a loss of focus. All of these teens/young adults suddenly living under one roof, it is asking for problems.
The LoS has a full roster but no major threats. When they do try to do any heroic-type work, they get lost in ego and don’t gel very well. The original team members and Brainiac 5 use a time-sphere to observe a young Superman (who is operating out of Smallville as Superboy). Note that the time-sphere will not work for anyone but Brainiac-5. They underestimate him and are discovered. They find young Clark extremely lonely. He can’t confide in anyone and no one can understand what his life is like.
They bring him back to the future with them (though they know this is a very bad idea). Clark really blossoms as part of a team in the 31st Century and wants to stay. A true threat (Fatal Five?) starts trouble. They are defeated but not in an absolute way. Clark realizes that he needs to go home to his family and become the inspiration that the Legion needs.
Irma (Saturn-girl) selectively hides his memories of his own future and they leave him with a Legion ring. Clark goes on with being Superboy but with a new vigor.
After Credits: Battlefield of WWII, there is pandemonium everywhere. As the camera pans through the area, signature sounds of one of the Fatal Five can be heard. Camera continues to show the area and eventually settles on a time-sphere. Inside is Brainiac-5 unconscious, one of the Fatal Five flies by.