The only people who called Gnostics heretics were the so-called church fathers, whose authority the Gnostics did not recognize.
Nor do I.
I respect their contributions, in some cases profound, but look to the actual words of Jesus, Paul and the Gospels for my beliefs.
Your choice of course, but Gnosticism is a recognized heresy by any Christian source. And the church fathers you referenced are long passed. And those were the Words of God, not gnostics.