Well, I wish you are right and the decline could be purely explained due to more efficient technology. Maybe that explains it partly, but here it's unfortunately mainly due to deindustrialization. And because Germany is not fully replacing the loss with less energy intensiv service business growth, I say this is a clear indicator for a decline in wealth.
Keep in mind, what happens when more efficient and affordable technology is available, the growth in usage tends to outgrow the savings in efficiency until the market is in equilibrium again.
Example: You switch from 1 standard ligh to 10x LED lights to illuminate the darkness better. In other words, when society is florishing, the energy consumption goes up.
Hence Kardashev scale is the best development indicator available. Seeing it in isolation for one country might be the real problem here, export and import of energy / products is not considered in the energy consumption chart for one country.
One day, the best indicator for the global economy power will be the #Bitcoin price.