IMO, if it was an event that had different sides that can win or lose, it would be much more interesting and enjoyable. Working for your preferred side till the event ends (completing missions, playing games, and then at the end which side has the most points wins), and then according to who won the story changing based on that.
For many events this is an amazing tactic and we take it frequently... an old example is the VS Event from 2017. However, sometimes we want to plan out further than the event for lore health reasons, so we need to have the "winners and losers" already planned out. Thus is the case here.