I'm already at level 14 with a legendary hero, when I attacked a level 10 base, I win but my wounded..

Its possible that the base you attacked had no defending troops to kill. They may have their APCs out, or deselected so as to not defend. Or they may have already been attacked and all their troops are wounded. You will still have casualties as the tower building will defend but you can't attack it.

Skill are generally random and will have a percentage chance of being used in a fight, some will not be used in the initial turn of a fight anyway or may only be used under specific circumstances. If you win easily because the enemy has no defences then you will not have enough turns in the fight to give your skills a chance to be used. Keep adding and upgrading skills and you will see them used at some point.