The mistake you and other anons keep falling into is thinking the message of the movie is something specific when it’s universal. When the movie came out, I complained about how the message of change made no sense because Steven was totally justified in hating what Spinel did to his life. But other people came to me to explain that it’s not just about Spinel, that any change to that perfect life where all his friends stay with him and chill would upset him. Spinel was used because it’s a movie so things have to be exciting, can’t have 1 hour filled with realistic problems in a musical with aliens. The theme of change is something the audience can learn: your life will never be exactly as you want to, you will suffer hardships but it’s ok, you can deal with them.
Future makes more sense as what would have happened if the movie never happened because then, yes, Steven would never learn any lesson about change and the fact that things don’t go his way will trouble him. But the events happened so the plot makes no sense.
Also, the audio leak hint that some other gems will try to kill him again, and if that happens all that of dealing with realistic down to earth problems will be bullshit as well.