There is no doubt that great thinkers existed before him, Pythagoras as you mention for example, but we are into the realm of maths here and not science with its emphasis on empirical data from observation etc.
Pythagoras made a direct observation regarding physical facts i.e. using empirical data:
A simple proof of the Pythagorean theorem involves rearranging four identical right triangles around a square formed by the hypotenuse. The area of the larger square (formed by the hypotenuse) equals the sum of the areas of the smaller squares (formed by the other two sides), leading to the equation a^2+b^2=c^2
But don't worry, I do get your point about dialectics and the fact that it thankfully ended up with Marx for a spell, if you see what I mean .