"Witch" makes sense. It's traditionally a role for women, and Ichi is unique for becoming one despite being male. The whole point is that he shouldn't be a witch, but he is. The title is communicating that.
You explained exactly why it
doesn't make sense. Yes, witch is a role for women. Yes, Ichi is unique for being a man who uses magic. The usage of witch here is completely inappropriate because the title
doesn't use witch. Your logic dictates that if it was a manga about royalty and it used "king" in the title it should be "queen" in English. No. That's stupid. Only someone stupid would suggest that.
Witch is the best fit translation of "majo," literally "magic woman." If the manga was titled Majo no Ichi, then Ichi the Witch would be correct. It is not Majo no Ichi. It is Ma
dan no Ichi. Madan is literally "magic man." It is an explicitly gendered title. The closest translation would be Ichi the Warlock. In modern English it has become somewhat uncommon to use warlock as a gendered term, but its origin waerloga explicitly refers to male magic users. It is the male counterpart of witch the way prince is the male counterpart of princess.
The correct translation is "Ichi the Warlock." You're free to disagree, because I do not yet have the ability to make people stop choosing to be wrong on purpose.