Back in the bad old days of only-just-emerging bitcoin ASICs, the equilibrium was distorted by the long lead times for new parts and relatively few suppliers. (For all I know, this might still be the case with new algorithms/new manufacturing process/ASIC generation).
Another interesting thing to consider is that rational miners will often consider applying their hashing power to the coin whose reward/block time/difficulty/exchange rate factor provides the best return (among those that share a PoW).
The fact that hash rate doesn't go down much during halvings or during market crashes indicates that mining is not in equilibrium. I don't think equilibrium has ever been reached since ~2011.
Another interesting thing to consider is that rational miners will often consider applying their hashing power to the coin whose reward/block time/difficulty/exchange rate factor provides the best return (among those that share a PoW).