When you fight two identical mobs and gaining 0 on the first and 3.2 on the second, you can't say it's not random.
Indeed, accuracy is a dice, but you can increase it, and have some sort of control...that you can't have over skilling-up.

Skilling up is as boring as obtaining a 5-percent-drop item on a weak mob. No challenge, ne reward based on you skill, just...dumb...luck.