“He should have simply said they misunderstood him, it’s not a chiddush, it’s accepted in every circle to ask a tzaddik to daven for us, and sourced explicit Chazal saying this.”
Youre misunderstanding. The chiddush is WHY its OK. Not the fact that it is OK. Chassidus goes into the Why. That’s why it’s part of pnimius HaTorah