First of all, he looks less than human and he’s faster than Barry and Jay.
He is so powerful that metahumans fear him and do whatever he wants.
He caught a bolt of lightning in mid air and repelled it back at Barry.
He grabbed a hundred or so speeding bullets in mid air with his bare hands.
Then, when Cisco shot him with the serum it didn’t work on him.
And this was after he proceeded to snap Barry’s spine, beat him to a pulp, stab him, and then parade his lifeless body around town like a trophy proclaiming his superiority to all Earth-1-lings in Central City.