So, then what level is the Tarnished, considering they beat Radahn and then also the only person to stalemate him?
By the time the Tarnished fights him, he's been severely weakened by the Scarlet Rot so his level would've been way lower during that fight. Malenia was equal to him in strength when they fought, and her level was definitely higher than his when she unleashed the Scarlet Rot.