There's initial capital expense, and ongoing expense. You're of course correct that the minimum capital is lower with mining. However, given a $75K initial investment, a miner has much higher ongoing expense.
My claim was that the lower ongoing expense of staking is compensated by lower rewards, so that both systems have similar profit for similar capital outlay. In setups where mining expense is almost zero, the higher rewards of mining give it much more seignorage than proof of stake.