Rich landowners were monopolizing land and driving small subsistence farmers broke because:

(1)Land can be bought and sold freely. Small farmers all vulnerable to natural disasters(flood, drought, etc. shit happens),often needing to loan from rich guys to survive, and more often than not, the small farmer couldn't pay off his loans, and would have to offer his land to clear the debt.


(2)There was a certain advanced farming technique that required large amounts of capital(meaning only for rich people), so the rich guys can drive the small farmers out of business with lower prices.


So even if the Han dynasty had a very low tax rate of 3%, the fruits would never reach the lowest class beacause the rich guys were playing monopoly. This problem would plague the Han dynasty till its end, and stands at the core of its fall.