EXos

-snip-

The one issue I had with it was that it was based on wisdom. Okay, that makes sense to a degree. However that made the wisdom stat much more critical than any other because some guy who had a high wisdom could become a master-sniper in a very short period.

I'd suggest linking only SOME of the skills to a learning rate based on wisdom, and others to a flat learning rate. I'd also include the ability to have mercs train to improve. Taking them out of the action for a while should balance this out. And don't allow continuous training, either allow 1 training to happen per time your merc 'levels' or prevent the merc from training again until he passes as many days not training as he did training.