Better on rewatch. Amazing, even.
When I was younger, all I noticed was the discrepancy between the Lilo plot and the Stitch plot. One was an emotional drama, the other a goofy space cartooon.
It is only now as an adult that I realize one fed into the other so greatly.
Stitch is alone in the galaxy. He knows he can only destroy, but he's looking for a greater purpose. Lilo and Nani are looking for someone to love, only to realize that all they really need are themselves.
Stitch is not necessary to the family. He knows this, and as the relationship between Nani and Lilo heals he decides to run away.
It is only when he meets someone capable of destroying this small family that he realizes who he cares about most. And he fights for it, in the most cartooney way possible.
This movie is not about Lilo or Stitch. It's about Nani's journey to appreciating both of these characters for who they are. When she realizes that Stitch cares about Lilo almost as much as she does, she helps him out.
Stitch realizing he belongs is a great emotional bonus, but I don't think it's essential to the story. But it works, and makes it better for kids to watch this movie. And I like it more this way, too :)