That's a good point about transactions. But are stock purchases included in the velocity calculation? From what I can find [1,2], money velocity is a ratio of nominal GDP to (either M1 or M2) money supply, and neither of these includes stocks or bonds.

[1] https://fred.stlouisfed.org/categories/32242 [2] https://www.newyorkfed.org/aboutthefed/fedpoint/fed49.html