So, you tried for the promotion but didn't get it. You explained yourself clearly. Your proposal was well thought out. It made good sense. But the leadership didn't go for it. It's possible they weren't ready for what you were proposing. It's possible they didn't quite understand the impact it would have so they preferred to not venture into unknown territory.
This does not mean you were wrong. This does not mean you didn't deserve it. This does not mean you missed something. This does not mean you're not ready for advancement. All it means is that the people in charge did not want to move forward. That is all.
It is not a waste that you took this leap. It is not a waste that you put the time and effort into your proposal. It is not a waste that after all that work, you got a big fat no. You will have learned something valuable through this experience. You will have elevated yourself in this process. And this path will open up somewhere else. Going for your dreams is never a waste. Ever.