@Count:
I know that. But the fact that it was kept ambiguous on the same level of Sanji's North Blue origins raised a inch of intrigue. And Chopper even got his own mini-flashback to explain Monster Point, so seeing a brief glimpse of Zeff telling Sanji to never hurt women wouldn't have seemed out of place in the slightest for the arc. If anything, it would have helped Sanji not seem so hopelessly irrational since a lot of people still criticize Sanji for that scene, and even Oda admitted that he felt uncomfortable writing it and really wanted to hammer home how Sanji is literally unable to hit a woman.
Also, there are several panels in both Baratie and the recent flashbacks of Zeff criticizing Sanji for ogling woman. While you can still teach someone to not hurt women while still be critical of being hopelessly enamored by them, its connotations still warded away notions of Zeff being responsible for teaching Sanji his chivalry. In fact, Oda was even asked in an SBS if Zeff taught Sanji his chivalry and gave a really vague non-answer about it (like he usually does).
There was really no point in hiding that Zeff upheld chivalry and taught it to Sanji. It's something that could have easily been assumed, yet Oda liked to sidetrack away from it for years as if this is a built-up reveal meant to spark at least some small bit of surprise.
what do you think that "zeff is a man among man" implied if not that he was the cause of sanji's inability to kick a woman?
it's more like a case of people wanting to see more when it's not there..much like makino's child being the child of "that man"