Aura steal isn't precisely 100%. What it is is it has a chance (fairly high chance on most stuff) to dispel and at 5/5 100% of the dispelled effects are transferred but if dispel fails 0% chance of course. Part of the problem is some buffs are basically undispellable and sometimes the buff move is several buffs so you often get just 1 worthless portion of it. Also if you steal an item you don't dispel....

But yeah I was mostly referring to the base abilities. Steal should almost always (or almost at least always on weak stuff) steal something in this day and age, despoil also steal something and apply debuff, mug always get gil. And they shouldn't have these effects as either or. It shouldn't be steal an item or buff it should be both. That's what I really meant by 100%