Instead of one skill being responsible for its own stats, a skill is separated into components(which affect all skills).
1.The Casting Spell(the Skill itself) which regulates only damage(of fireball and its splash damage)
2.The Spell Projectile Skill: Increases Speed of projectiles(fireball travel speed).
3.Splash Damage Skill:fireball splash damage area of effect, as well as any spell with splash damage
4.The Cast Mastery skill: which reduces cooldown for all spells(including fireball).
5.The Time Control Skill: increase duration of spells(fireball splash burning duration in this case)
6.The Mana Mastery Skill: Reduce mana consumption of all spells(fireball cost)
7.The Range Mastery:Increase range of ranged spells by N each level.