In the 18th century, it's conscious beings competing against conscious beings. There is no reason that needs to continue to hold. Once all the problems for general intelligence to solve have been solved, only something on the level of expert systems will be needed. Or something else will become wasteful. Maybe the most efficient things will be minds, but they will be cold, dark minds - they could easily lack love, curiosity, boredom, play, or other fundamental human values. They will have no surplus, and so no leisure.