You're right that, purely in USD terms I would come out ahead just purchasing BTC.

My considerations also take into account increasing my experiential capital, investing in energy resilience and abundance for my family, the value of the heat produced by the miner, and satisfaction I get from participation in the network.

The s9 is used as a space heater in a cool room in our house, so the BTC mined is essentially a rebate on power that would've otherwise been consumed by a resistive heater.

The short answer is, I don't need it to ROI in a certain amount of time. The miner is always available to turn excess electricity into BTC and heat. If I want to use the electricity the system produces for other tasks, the miner simply ramps down until there's extra electricity that needs a consumer.