I am going to leave each one of the classes descriptions and I will try to explain why I claim this.
Battlemage
Health 50(+5 Per level), Energy 50(+5 Per level)
Weight of Equipped Armor is reduced by 50%
You can cast spells with both hands
You gain +10 Protection and Resist All +10 when equipping a magical staff or an orb
Wizard
Health 35(+3 Per level), Energy 50(+7 Per level)
Willpower +2
Can cast with both hands
I will now make an example with both characters being level 10 without getting anything that would increase their attributes.
Battlemage(lvl10)
Health 95, Energy 95
Let´s assume also that you have a magical orb +10 Protection,+10 Resist All
Health Difference +33 Energy Difference -28
Wizard(lvl10)
Health 62, Energy 123(also adding +10 from +2 willpower)
Health Difference -33 Energy Difference +28
Now let´s think about this for a moment, Battlemage has a higher hp pool and Wizard has a higher energy pool, Willpower will in no way shape or form influence the amount of energy of you gain per level, only energy regen.
Now hypothetically you would assume the wizard is a better caster than the battlemage, but this is only true in the first couple of levels, where the energy difference is much higher, once you pass a certain stage, the battlemage surpasses the wizard in terms of overall tankyness, the thing about this, is that the Mage classes are only as good as how long they can last in the battlefield, the extra energy and the +2 willpower that you get for the wizard are completely useless in the sense that they become redundant later on.
On these specific stats, I did not even give my examples +5 Vitality or +5 Willpower or even the traits, if I did, the value differences would become very insignificant and they are already insignificant if you factor those bonus attributes and traits, but the thing that makes the Battlemage better in all scenarios is overall Tankyness and the ability to be as good as a Wizard in most stages of the game.
The main issue with the Wizard class is that it offers next to nothing that you can easily get in the game or by fiddling around in the character customization screen, at no given point do I feel that the wizard is better, why would I want a squishy caster when I can get another class that does exactly the same things at the same level of efficiency and a lot tankier?
If by any chances, the wizard would deal 5-10% more damage with the spells, then the Wizard class would become much more desirable, but in its current stage, the Battlemage will always be the superior Mage class.