If you're referring to the underlying rigorous analysis / set theory / foundations of math, it's arguably still easier to understand now that those things have

If you're referring to the underlying rigorous analysis / set theory / foundations of math, it's arguably still easier to understand now that those things have been developed. Before these theories existed, your only way of truly "understanding" calculus to a similar level of detail would have been to actually develop the foundations of math, which would be impossibly hard for most people.