Happens.
It's nice if you see him as an allegory about immigrants, but look at it like this:
He doesn't fail. Not once. I know I stated this before often enough, but it stays how I see it.
Everything he tries he not only succeeds at, no, he also reaches heights noone before reached. He impresses everyone (except the bad guys). Everyone (again, except for the bad guys) loves/admires him in the end. For his wisdom, for his skills.
Unless of course Sir Terry tried to see how many deadly sins of writing he can put into a novel before people would call him out for it, this character is everything but well written.
He is young.
Yet he can do so many things without any real explanation. What we get as one from the story 'he read a lot and an Igor showed him some things'.
Great, really. Pick a random book from the fantasy shelf and chances are high your maincharacter also can do things beyond imagination with equally thin explanations.
And to make matters worse:
He's a character that has no path before him. As he has already proven infallible. Would you really want to read a book of 400, 500 pages about a character who fails only at failing?
I am judging the book by the standards I know from Discworld and by what I learned about writing. And I stay with my point: There is NO need for him to BE perfect instead of just thinking it, trying and failing.