Right, and that equilibrium is determined by the cost (both hardware and electrical) of running whatever the widely available 'best' is.
Miners will find their way to places where electricity are free. Eg. solar panels for mining. In the long run the only factor impacting profitability is the trend in BTC value.
And economically speaking profitability is supposed to trend to zero in any type of competitive market.
Solar Panels are not free. They have a capital cost and a life expectancy. They require maintenance and upkeep. They provide very little usable electricity in cloudy weather, and none at all at night. These peaks and valleys can be smoothed out by generating more than needed and storing the excess to be used when output is low, but that process also has associated costs. They may be low cost in the long run, but they have a cost.
hash rate per joule will always be a factor in mining profitability.