But Heraclitus, for instance, was contemporary and accused him of plagiarism and trickery. Why abuse a person that doesn’t exist? Ion of Chios was contemporary and said that he authored Orphic hymns.
The Orphic hymn to Apollo proclaims “your resonance attunes the whole globe”. Now, we don’t know that Pythagoras wrote that. We can’t prove that sort of thing. But it sure seems Pythagorean.
Did you know that Copernicus, Kepler, Galileo and Newton all claimed to be Pythagorean?
The man is a legend. Embrace the legend. He wrote lots of things down but he either destroyed it to avoid creating a doctrine or it was destroyed during one of the different massacres of Pythagoreans. Because that happened.
No one is denying that a cult named the Pythagoreans existed, that many of their writings are preserved, and that they influenced Copernicus etc ...
Heraclitus was notorious for his cutting critiques of predecessors. There are a total of three very brief mentions of Pythagoras in fragments of his work (fragments 40, 81 and 129). This is not really enough to go on - it's not clear whether he's criticising someone he's met in person, some learnings that he's heard through a third party, or a cult figure that was invented and idolised by the Pythagoreans.