I think this reasoning (that is, doubting PoW value like that) is wrong. The problem of "conventional banking" is not in said overhead.
It's wrong to compare an average bank electricity consumption, plus it's workers salary with Bitcoin/PoW alts consumption.
Bitcoin doesn't eliminate banks. Banks are the ultimate liquidity providers to enable capitalism. FRB evolved because the demand for money exceeded the supply of gold. Should Bitcoin become the dominant currency of the world, banks would need to apply FRB to it as well to help control the price or risk massive waves of bankruptcy in a deflationary event. The alternative is banks won't touch bitcoin. Without demand for bitcoin investment capital, it will likely always remain niche.
Well, either banks can apply FRB using Bitcoin as "reserve currency", or there could be alternative to banks represented by alts. Obviously, alts are not mature right now for that, but that doesn't preclude them from solving the power vacuum problem in the future (I mean, more broad power vacuum problem than Bitcoin alone already has solved).