Jesus often deviated from the OT law in his own teachings, for example telling people that they shouldn't worry about what they ate and what they wear

Yeshua never said that the laws were annulled (and certainly wouldn't have referred to the scriptures that he based his life on as the "Old Testament") - his teachings were that the emphasis should be on morality and ethics, rather than judging people based on their level of strict adherence. Those kinds of teachings exist in various groups in every religion, but don't indicate that he considered the laws of his religion to be annulled.

Jesus specifically said that he had come to fulfil the law

Every judge in every court says that they come to fulfil the law - that means that they consider the law to be above all, not that they consider their personal actions to have served the purpose of the law, and the law now becoming obsolete. (By the way - have you studied the Greek scriptures in their original text? It seems that correctly interpreting that phrase requires a proper understanding of the phrase and context.)

Some of it from leadership was against it for the purely religious reason of Judaism leading people away from salvation.

And most of it was supported by leadership of the Christian churches and institutions, for that same reason. And are the Roman Catholic Church, the Eastern Orthodox Church, and the Lutheran Church - all of which expressly persecuted the Jews in their countries - a minority among Christians?

they considered God to be the same God.

1 ≠ 3

You cannot make the argument that it's cultural appropriation if it is the culture itself that made the sharing.

After they negated the laws and beliefs of the Hebrew scriptures, and considered those who followed them to be objectively wrong, they very clearly left that culture, and can't be seen as a continuation.