We're talking about just keeping track of who owns what amounts of a commodity. That part is using terawatt hours per year! I am very doubtful that the "keeping track of who owns what amounts" part of the stock market is anywhere near that.
Determining who has the rights to make changes to what data, auditing changes, auditing ever-changing access control rights, systematically changing these rules to adapt to technological advancements, etc. is the function which Bitcoin accomplishes that you are discounting from your perceived cost of the traditional stock market.
We're talking about just keeping track of who owns what amounts of a commodity. That part is using terawatt hours per year! I am very doubtful that the "keeping track of who owns what amounts" part of the stock market is anywhere near that.