I guess the two things are complementary, if you don't have slaves, it creates a greater incentive to search for technologies that amplify human labor. So in a

I guess the two things are complementary, if you don't have slaves, it creates a greater incentive to search for technologies that amplify human labor. So in a sense both explanations might be true. If there hadn't been any slaves, the question of "how can we build more durable gears" would have been on more people's mind, which could have lead to better metallurgy earlier on, even without guns/gunpowder or whatever lead to the need for better metal in the enlightenment?