Oda didn't put a flashback showing who taught law to use his devil fruit, I mean it seems difficult to learn how to use a devil fruit Cora: "It doesn't work like magic!" Tell me what theories you guys have.
But it is much harder to master. Luffy's df is basically "get the most force in a single punch, by stretching/spinning/haki", whilst I believe years of training are required to perform a single accurate Shambles. Do not forget he learnt to be a doctor Simultaneously.
