I see. You have a good point there. But if I have to say, I think the magic in the DB universe is far more easier to use or at least to get access to than it is in the FFverse. While Buu was able to tear apart dimensions just by screaming, it was a simple fact he was already a magic based being to begin with.
- Boo is not a magic based being. The fact that he has been created through Bibidi's magic has been retconned already. Boo was just an evil force roaming the universe.
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So fighting him would've the equivalent of fighting a final boss or partially god of magic. Though Whis can remind time, Ultimecia can compress and destroy it, along with all of existence itself.
- Ultimecia cannot do any of this. The mere fact that she is stuck in a loop in which she can never succeed doing more than she was able to in her true form (that means a partial time compression) shows that her powers are very limited. Ultimecia is still bound to causality, even if just to an extent. Whis is not, he lives totally out of the realm bound to logic. Ultimecia's plan was to reunited Hyne's power in her own body to become the equivalent of the Sorcerer God and she failed and is bound to always fail.
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Yes, Ex-Death had to get control and use magic to manipulate the Void and use to turn any dimension into a death land but that alone may put him on par with Buu.
- But Boo does not do that with magic but mere force alone, expressed by a scream. That is what I am talking about. Dragon Ball does not need any character to get access to some special hidden power. And in the end they are also not actually comparable. When it comes to powerful wills, the only character with a really powerful will that was ever totally fleshed out is Sephiroth.
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They just have different means of accessing their powers. When you think about it. Both series intepretation of magic is overkill. But I have say with FF and things such as Gods that eat entire universes, instant death magic, star and galaxy busting magic, and magic that manipulates the very fabric of space time itself and uses it against you may just be a tad more overkill than DB. Though Whis and Beerus may have the potential to do such things too, but I have yet to see them create a black hole from nothingness and use it to destroy everything. If you had to rate any Final Fantasy villain's power level then Ultimecia and Ex-Death are definitely going to be at the top.
- Magic is not really interpreted that overkill in Dragon Ball. It just exists and either works or does not. Most of what they use is Chi and that is not the same. There is powerful magic but most of the greatest powers are not magic. X-Death never created a Black Hole (he could do something similiar, though - and that is not impressive for Dragon Ball because the characters can escape from the Event Horizon), he summons a force that imprisons someone in the "Void", something that does not actually erase your existence but is also itself another pseudo-dimension where nothing exists except what you have imprisoned in there. So X-Death imprisons someone somewhere where they can break out. Like Gotenks and Boo did. The only possibility for them to not stand a chance is if they are not immune to a possible time freeze that could be a continuous state in this void. And as said, Ultimecia is just as powerful as she has actually come far. Not very far. The Time Compression could not full work. They are some of the tops but not THE tops. As a matter of fact, the probably cannot even closely compare to an entity like Bhunivelze.