It is a wasting because it could be done with staking, that way the could shouldn't need miners.
Yes, but it could end up making Bitcoin centralized. Think about it. Imagine being a huge exchange with a lot of PoS coins in custody? Solely from being a whale, you automatically have a significant influence over the network. In contrast to PoW whereas you'd actually have to dedicate money to buy hardware.
This is a fair point. PoS is not better at everything, just like the Lightning Network. Moreover, I don't think the attitude of reducing electricity consumption is something we should adopt in general as a strategy to fight global warming. Reducing waste makes sense, but energy consumption seems to be something different. Perhaps it's just because I was influenced by the idea of the Kardashev scale where energy plays a crucial role. I am not a climate skeptic, at the same time, so I think that something should be done. Namely, we should work on clean energy solutions. Some research suggests that mining largely uses clean energy, by the way.