Mythic Weapons really should be the Apex Weapons, however, we don't know what they have planned moving forward with the iLvL system.
I would imagine that this is not the last time the Mythics will be adjusted.
I disagree with reducing/removing the MAB on the staff, but the enhances Elemental Seal can go away in my opinion.
Sense I sadly have never had one of these (yet) I do not know if there is any hidden +int on it, but some thing that could improve imo is to add some INT to it to help put that distance between the monsters and the cast giving the spells more dmg. Adding a Elemental Magic Affinity +7 would def be a good idea as you stated. We as blm don't need aftermath that is attacks twice or thrice, why not make the aftermath reduce elemental magic casting speed and/or reduce MP cost of elemental magic by 20% or something along those lines.
:3 that is my 2 cents about it :3 I have tried to work towards this mythic several times, but sadly never could get a group to help, and now that you can basically solo it I don't have the time to play lol maybe one day I'll have it maybe.