Obviously in really decentralized environment any peer-to-peer action (transaction, messaging, video streaming, whatever) does not need any "consensus" or other kind of approval from the third party. The only concern is a double spending problem but 1st)-blockchain and PoW does not 100% guarantee to avoiding it, and 2nd)-it might be resolved by the other means, than just burning the electricity and warming up the air.

Unfortunately bitcoin by it's nature has only imitation of decentralization. Moreover, what attracts most people to invest into bitcoin, it's mining, etc, is an idea of making money from it. Since last word of PoW is "work", it gives an illusion of something useful, the work cannot be useless, people think. Thus it puts PoW virtually far advantageous over PoS (since PoS is naturally the same as paying interests on money lending without investing those money anyhow into the real economy). Without rewarding for mining nobody will spend thousands (and probably even millions) of dollars/yuans/euros/pesos, etc. onto the hardware and electricity.
Yes, and this is exactly what is going on with bitcoin.