It's a distinction without a difference in this context. The "Calvinists" came to the same conclusions about power as the Enlightenment scholars did (namely that it should be limited, distributed, etci), except two centuries earlier. The real point of difference between Rome and the Reformers was the nature of man in his pre-fall state. The Reformers' point is that man is already corrupt even without power--but only the most pedantic would disagree with the point of Lord Acton's quote.