Disregarding the quibbling about what is waste and what isn't, there's a difference between the work done to validate blocks and work done for the PoW based Nak

Disregarding the quibbling about what is waste and what isn't, there's a difference between the work done to validate blocks and work done for the PoW based Nakamoto consensus. You want block validation to be as fast as possible which is a separate concern from deciding on a chain which is where you want lots of work.