If the tax is based on a percentage of the transaction amount, then the number of transactions is irrelevant.
The average size of transactions increases with wealth. It's the difference between the cost of the Chevy and the cost of the Rolls.
That point is still valid, however: the consumption levels of the one with $50B is approximately the same as of a person who has only 1B. Since consumption is not proportional to wealth, the use of it as equity measure is problematic.