You can expand and contract the 'stock market' to whatever shape and energy density your argument requires. Does it include all the energy required to keep alive the people who work to sustain it? Does it include investors, the wealth it generates and all the super yachts bought with it? Or on the othet side, is it just the near energy free idea of what the stock market is?
If ethereum ever achieved adoption even close to a fraction of what stock trading has, then you'd have the same problems and overhead.
As it stands, the apples to apples comparison has any centralized, trusted network being more efficient than [attempted] trustless, proof of work like ethereum.
That's because you don't need the same scale of people to run a cryptocoin. It does it itself, more or less, with some maintainers. You can trade value with anyone anywhere in the world without all those banks and people. So in this case, it's an extremely important point.
