If EVERYONE uses this logic, the difficulty adjustment will ensure the “profit” from operating a rig(s) won’t cover the capital cost of the rig(s).
That is dependent on the operational lifetime of the miner, the transaction fees at the time of operation, and the dollar price of Bitcoin (assuming the energy usage is priced in dollars).
Additionally, the dehydrator I built is a fraction of the cost of a dehydrator of comparable power one could but from the store.