Actually, you summed up the 15 actions pretty well in your opening statement

Fun to play - With fewer abilities, they can make them all worthwhile. Cant count the number of times I levelled up on CON and thought "wow, wonder what i get in another 2 levels cause thats piss."

Different enough from each other - unlike now where many abilities on melee classes are pretty much the same, or share animations with other abilities, this will no longer happen. class uniqueness is pronounced when the abilities are fewer and more useful

More or less balanced (can't have too strong and too weak classes) - by giving each character a set amount of skills, no one class will be more or less capable of coping in different situations. A mage with a skill for every possible outcome is more worthwhile that a melee that only has 1 avenue of abilities. By reducing them down to fixed amounts it will make balancing easier.