Reversing the order here a bit I know. Please bear with me for a moment:
Yes, by definition. We are talking about a game about fictional characters in a mythical (european) setting.
Further more, we are assigning simple numbers to not-easily-quantifiable attributes of imagnary people.
Everything about it is by definition an assumption.
This is our assumption.
Written re-troactively to justify the characters in the core book? Perhaps.
But it is our assumption.
I would argue that every character in the core book is build on the assumptions made after hours and hours of play in the 4th edition.
Yes, they follow 5th rules, but they are in many ways 4th ed characters.
I call it an artifact because in 4th ed (as you may recall), intelligence was the be-all-end-all stat for magi (not my words, see this thread) and so the example magi are made with very high intelligence.
And here you are largely arguing my point - that the very high intelligence is less than necessary in the 5th edition.
Also, I believe the average I've seen is a gnat's whisker above 2, on the average.
Haven't crunched the numbers though.