The Warmage: a Simple Caster (TM)

[Pramxnim]

Saving throw proficiency in 5e is divided into 2 types, and each class is only proficient in 1 save from each type. The more useful saves are Dexterity, Constitution and Wisdom, since more spells and effects target them. The other 3 are targeted much less often, so they are generally deemed less useful.

Since your class is already proficient in Constitution saves, I would hesitate to allow it to pick up proficiency in Wisdom saves as well. I know it breaks up the symmetry between the 3 styles, but otherwise the style that gives proficiency is Wisdom save is just more desirable than the other two from a mechanical standpoint.

EDIT: I just read your note on the Sage style, but I still think it's a good idea to avoid Wisdom saves here. If you find it impossible to reconcile the two strong saves vs. casting stat association, I think it would be best to abandon the sage style altogether.