Being ten years old in the Pokemon universe doesn't mean the same thing as being ten years old... well, anywhere else.
I'm not sure what your argument even is anymore. Let's drop it.
In conclusion, I think it's safe to say the Xenoblade crew takes this, with Arceus as a possible second opinion albeit with a lack of evidence behind it.
However, even if we assume that Arceus does have the power to destroy the universe(seems very unlikely), which would put it on equal ground with Shulk, Shulk would still win in a straight-up "battle".
The battle would consist of "who destroys reality first", but Shulk can see his opponents' actions before they happen, so he would always beat Arceus to it.
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