Have you seen Stardust? It's the exact same movie as 5th Element. There's a super powerful woman who is useless until the end where she won't use her power until the lead man tells her he loves her, then she unleashes this armageddon that would have come in handy earlier. (Although, in 5th Element she couldn't have unleashed it earlier, but there's no excuse in Stardust.)
5th Element is just plain awesomeness. Why aren't you watching it right now?