If there were a way to provide that level of security without sacrificing decentralisation and without using that much energy, we'd look into it.
(this is not a rebuttal/opposition, this is adding detail/context/proof that we already have "looked into it" and found a way, as proof of and agreement of what you are saying)we already found it the answer to the "energy waste"
.. imagine if we wanted the 200exahash security level we have now.. but were still stuck on wasteful CPU hashing..(like many silly altcoins)
the energy wastage of that would be hundreds of millions of PC's..
we found the solution. .. GPU's,, and then found a better solution again.. ASICS.
the watts per hash efficiency is super efficient
back just 12 years ago
a 100watt PC draw = 10mhash
today a 100watt draw = 4,600,000mhash (3kw for 140thash = 100w for 4.6thash)
that is 460millionx more efficient than a PC CPU
the metal hardware production saving alone is another efficiency too..for asics
worded the other way: 30 PC's of equivalent 3KW draw only gets 300mhash compared to 1 asic of 140thash
..
as for the decentralisation of the blockchain data.
asics have no hard drive(they dont touch chain data) so the hashrate and electric rate do no affect the decentralised archiving.
changing the hashing speed or the electric used for mining does not impact the blockchain decentralisation so mining again has no affect on the "centralisation" of block data..
asics can move pools and distribute themselves in 5 seconds. so even the 'pool' centralisation factor is not an issue. they are not fixed or stuck only operating within one pool