New Heal Formula

Many people don't start perfect and until the MTS came out, can't afford to reset that stat to four. Even with MTS out, some people refuse to reset it, thinking that it takes too long to merchant.
Then some have zhelms and some don't. The extra 13~17 DEX from that zhelm might add damage. The horntail pendant, which adds yet another 21~23 DEX may make it worthwhile investigating.
It's like Dits and Shadowers getting more Atk from a zhelm because of the STR on the helmet.

Nothing you said matters. The point still stands that there is very little difference in dex between any Magicians, and it is illogical to think dex might do something like that.