Martin Luther King "stole" Gandhi's arguments and strategies, and was killed in a pretty common way...
Would you hold that against him when measuring his impact, too?
Original or unoriginal, Jesus has had the bigger impact, no question. Descartes' attempts in the Meditations to prove a just God existed might not ever have happened had not Jesus did what he did to make what would become Christianity the dominant religion in the West for 2,000 years.
Then there's all the negative that came with Jesus--2,000 years of bad luck for the Jews, the concept of a hell and punishment after death (which isn't really delved into all that much in the Old Testament, that's far more a New Testament/Christian ideal), and you can pretty much just fill in the blanks from whatever Pat Robertson or his like have said or complained about lately.
By contrast, Descartes is the father of modern philosophy...but ask yourself--
How many people does philosophy really reach? (And remember, *I'm* the guy who back in the day posted "Philosophy Weekly" threads, and I'm saying this.) ;)
With the possible exception of Marxism and a couple others, philosophies in the West have almost always been more of a upper-middle to upper class endeavor...ask the inner city kids of the LA Unified School District (notorious for being both one of the largest and worst school districts in the country) and see how much the kids in it and those educated by it know or care about Plato, Aristotle, Descartes, Kant, Nietzsche, Heidegger, and what have you.
THEN ask them about Jesus, and see what kind of responses you get.
Like it or not, for good or otherwise, Jesus just has the bigger impact, even today.