To real skill usage for NPCs, NPCs certainly need stats.
However forcing the scripters to specify all stats for a skill feels a bit cumbersome for me.
And do not forget, there are several possible data that skills might use beside stats. It involves crit, dodge, def, atk, matk, items etc. Some of them can not be manipulated by stats, such as the item part of def. Some skills are use certain item stats to calculate their formulas. I see this feature as the source of many troubles. Some skill may not work as expected this way, or cause crashes.