I was confused about that too. Those effects are not under the Skills tab. They're considered Status effects and they're under the Basics tab, along with the debuffs like Poison etc. Basically, if it shows up in the skill list of the character, it's going to be in the skill list. If it shows up in the Effects bubble up top, it's going to be in the Basics. Though there seems to also have been some confusion with the terms, because it looks like the Berserk effect was translated as "Uplift" in the Effects bubble.
In any case, Berserk increases Atk and Crit by 2 per level, and decreases defense by 2 per level. Berserk II basically gives 4 atk and crit, and decreases defense by 4. It can have its perks if you can mind the defense penalty.