You've lost sight of the point again, it's not about how strong Zoro and Sanji are but rather the gap between Luffy and their opponents.
You were on the right track with Big Mom, because the gap between Luffy's opponent and Big Mom was not heaven and earth like Kaidou and the commanders, she was taken down by unorthodox opponents in an unorthodox manner. Even if Kaidou was much stronger, it was close enough to throw the structure apart.