...if we were wasting so much power, ...
Perhaps you did not catch the implication in my post about five posts upstream. Moving from fiat to bitcoin likely saves power. At least one-point-twenty-one-jiggawatts (I guess the appropriate cultural reference today would be 'Over Nine Thousand !?')
But if we never found new ways to generate masses of power we would probably see a freeze in bitcoins.
That's not how difficulty works. Even if we were power limited, we would approach that power limit gradually - perhaps asymptotically. Increases in difficulty would then slow gradually - again, asymptotically - to match the collective hash power of the network. When hash power stops increasing, difficulty stops increasing. Accordingly, blocks would still be found on average every ten minutes.