Is the saying "Beating is not upbringing" - when intending excessive beating - contrary to the the saying of the Messenger of Allah, peace and blessings be upon him, and is the one who says it sinful?

If the person who uttered the phrase meant severe beating, then his statement is correct, for severe beating is not a means of upbringing; it is oppression and assault. As for non-severe beating, it is an educational means mentioned in the Quran and Sunnah, and it is not permissible to deny its being an educational means for one who knows that, otherwise he would be sinful. The ignorant should be taught about this matter.