In my post about the battle of Telmarion i improvised that battlemages made gusts of wind, shot fireballs at incoming projectiles or made some sort of force screens.
Since no one claimed that wasn't correct i assume that is the case with the battlemages.

Dunno if a group of battlemages boosting a group of infantry is the end all be all winner way.
For one, it's not the way the armies deploy them, which should be one hint since at least someone would have thought about trying it. If it was the best option, everyone would use it.
The other thing is that great, now you have powerful infantry. However the battlemages are now preoccupied with enhancing the troops and won't be very good at defending against projectiles from enemy bows artillery or battlemages.

Of course, it depends on the situation. If the enemy force lacks ranged elements, i'd say go nuts!

I once more realised that the Steel fist also doesn't have any battlemages of their own.
No matter, just push through with sheer force, that should show those pesky battlemages!
(I am just bantering, again in the post, i describe how the battlemages save Claus's vanguard from being completely decimated by enemy spellfire with effective counterspells.)