Yea but Kaidou said himself he wasnt serious for a long time and Luffy was the only one managing to do it currently, imo just implying that BM fought against a non-serious Kaidou really. Furthermore, BM's CoC performance vs Kidd-Law wasnt good enough, her CoC Coating seemed to have depleted since Oda didnt even depict black lightnings or no-touch zone in her attacks even after she had turned into Bigger Mom who is guaranteed to be her strongest form. While Kaidou is currently partying around and spam CoC Coating every second, so i think current Luffy who contends with serious Kaidou is surely stronger than BM who depleted her CoC Coating against Kidd-Law