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Yeah... experience matters and Sauron has that in spades over the Lich King. That's not to say that he couldn't put up a fight, though. I think the fact that he couldn't figure out how to destroy The One Ring helped a ton here.
As for the next battle - I know Deku has the power of All For One now, which is the strongest quirk in MHA. Is that quirk strong enough to defeat whatever powers Asta has?
As the show progresses, it's shown that...
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Deku has more than just All Might's Quirk. He has access to all the past users of One for All's Quirks, which is 8 of them.
...and Asta (from looking up what he can do), has the power of Anti-Magic, which is said to nullify magic. It's been stated in the DB with Todoroki before that Quirks are NOT magic, therefore I don't think Deku has to worry about losing that. That's also not to say Asta's stomped out completely, since he does have strength values too, especially with that sword of his. I'm assuming it's all the matter of who force their power's timer down first.