Fair points and a very well constructed argument.

The thing is, how do we ensure the security of a chain without wasting this much energy? I mean, if we don't care about the decentralized aspects of Bitcoin then we probably shouldn't be using it after all. So since we do care about its decentralized aspects.. how do we make this possible?

Since there's no known better technology than Bitcoin/PoW, this is simply the best we can do. There is enough time for open-source to be explored and to make Bitcoin better as time goes on. But the issue is, the Bitcoin community generally doesn't like changes. Therefore, even if we did find a better alternative to PoW, chances are it'd be instantly rejected by the crypto community.

This thing is double-edged. You have a currency that needs upgrades but upgrades mean acceptance, which this particular community doesn't agree with very well.