THANK YOU ROSS! But I still disagree with the stun thing... STUNNED MEANS BY DEFINTION: To deprive of consciousness or strength! So moving and attacking would go against stun because the FM would still have it's strength and consciousness to take actions. I think Relentless should be removed. I'm sorry, but this just won't due... Btw I AM A GRAMMAR NATZI! You can probably tell

This is precisely why the Relentless rule has been modified the way it has: to maintain the purpose behind "Relentless" while better balancing it to eliminate unfair advantage.
The Fighter Mage is intended as a front-line combatant. This is why the "Relentless" ability was given to him in the first place. The greatest risk a unit has being within close proximity to an enemy is being trapped and unable to react.
Immunity to stun prevented the trap, but it also gave Fighter Mage some unfair assuredness that his "on the fly" spell casting ability could never be taken away. This advantage is particularly unfair in maps like Circle of Slaughter where proximity to enemies isn't even relevant.
In other words, the strength of the Fighter Mage's ability (as Dies best puts it) is his ability to remain untrapped- to move in to attack and move out if necessary. Immunity from losing spell casting ability is what was over advantageous about Relentless.
From an artistic character perspective, the new role also better fits the archetype of Fighter Mage. When hindered by a trap (stun) he falls back on his instincts as a physical combatant- his abilities to move and attack viciously - rather than the crafty ingenuity of spells.
From this reasoning, I can foresee new abilities for the other mages, such as "Can cast manipulation while Stunned" for the Wizard, and so forth. Depending on how well received the idea is, we might see these injected in future updates as alternative "swappable" powers as the game evolves.