Even if we believe that calculus satisfactorily solves Zeno's paradoxes, we can't earnestly say that conceptual clarity was achieved before Cauchy's definition of the limit in the 19th century.
For Descartes, there was only some very non-rigorous proto-calculus (as we know, he himself made important contributions).
How was this acceptable for Descartes?
He himself didn't like infinitesimals - in differentiation.
Unsurprisingly, since the concept behind dx/dt is extremely confused and vague (not talking about modern rigorous reformulations). Far removed from being "clear and distinct".
But this just means that there was no solution available to him. Just doing differentiation algebraically by unproven rules is even worse and reduces the mathematical treatment of motion to guess-work.
Did Descartes ever defend his choice to accept something as muddled as motion in his philosophy? Something which contemporary mathematicians had just an inchoate understanding of, and handled in a mysterious, "occult" conceptual framework?
Zeno's paradoxes, at the very least, show how much humans struggle with the concept. He couldn't have claimed that we simply possess a clear and distinct idea of motion.