“And I think the first one to claim there other legitimate leaders of Benei Yisroel at the time of Moshe Rabbeinu, was none other than Korach”
Not that there are other legitimate leaders, no one denies that the Shvatim or Aharon were leaders. Korachs claim was that there can be more than one Moshe Rabbeinu per generation, or that there is no need for one at all and everyone can be equal. Yes this is a very important point.