If thats the case why did Jesus not debunk the whole of hebrew scriptures, that portrayed god far different from the loving merciful father jesus tried to show?
We makes you think he didn't?
He said it often: God wants mercy NOT sacrifice, Love your enemy, do unto others like you woudl have them do to you, forgive and don't judge, let he without sin cast the first stone, man is lord of the sabbath not the other way around, etc, etc.
He didn't debunk the WHOLE of Hebrew scripture, he put it into perspective and put what was man made doctrine in the light it need to be put and left the rest to us, we either follow one or the other, as always the choice is ours.