I don't see how it's arguable. Newton formulated the law of gravity, he perfected the laws of motion, and he invented calculus. Einstein was great, but not as key as was Newton.
But according to the very same Royal Society, of which Newton was the president at the time, Leibnitz was a thief. Along with this poll I wonder if the concept of "conflict of intrest" ever occured them?
As far as who is responsible for the spread and wide acceptance of Calculus, it was Leibnitz and the Bernoullis who deserve all the credit.
After Newton, Calculus was dead in England for another ninety years, in part due to Leibnitz-Newton controversy and also due to the needling of Bishop Berekley at the shaky underpinnings of the subject making the English eschew analysis in favor of classic geometry. Math major here. :)