It is not about discoveries but the ability to stack them. Newton indeed stood on the shoulders of giants. But there is no reason to believe he was the first or the only one to come up with the core ideas of calculus. There probably was somebody in Kerala, Tobolsk or Nairobi thinking about these things but leaving no notes, using a rarer language etc. But Newton was the first, whose work was picked up by a wide body of researchers and rapidly developed further. For whatever reason (the Brits did not get there until much later) the Kerala school was not successful at sparking that uptake. Unfortunately the history is full of brilliant people who simply aren’t at the right spot at the right time. This is true in the west, too, by the way: the story of Scheele, for example