This bothered me too. The Altmer takes 2.5 x the damage the Breton does. Altmer damage taken from a 100 base damage fire spell is 100 * 1.25 = 125. Breton damage taken is 100 * 0.5 = 50. 125/50 = 2.5. In the language of the article, it's "150% more damage," not 75% more.
