Firstly, nobody believes that Proof of Work is here to stay - it's bleeding money from the currencies that use it at an astonishing rate, and as soon as Proof of Stake (or other algorithms) can replace it, they will. PoW is a direct financial drag on these economies, and it will not last long. Bitcoin will probably take longer to clean up its act than Ethereum, but that's largely for political reasons, not technical ones. Technically, it should be a lot easier to do than Ethereum, in fact. (It helps not being nearly Turing complete.)
Secondly, brute force is how things begin. The Unix philosophy has always suggested using brute force first: premature optimization is the root of all evil, as they say. We are at the very earliest stages of designing global public heterogeneous parallel supercomputers, and we should not be surprised that the early approaches are brute force.
It won't be that way for long.