I have a rogue with a legendary Air Archon. It has 21,000+ for some of its stats. It is in the mystical companions, which i have at 13% boost. I also have a legendary Siege master and legendary Sellsword on the same character, both in the fighter companions (13% boost) and they have the similar 21,000+ for their stats. I think the bonding stones are 13s. This toon has the purple companion equipment.
I have a hunter/ranger with a legendary Air Archon. It has only 17,000+ for its major stats. (13% bonus in mystical category). The ranger is not as high of a level (level 80, but not above 17,000) and the bonding stones are 11s, not 13s. It only has the blue companion equipment.
I have an SW with a legendary Mini Gond. It has rank 11 bondings with blue companion gear and 12% boost. The max stat is just over 14,000. Other epic mystical companions on the same toon have higher stats. btw, I don't think i saw a 10% increase in stats when I promoted my miniGond to Legendary--maybe a 5% increase.
Is there a reason that the augment is significantly lower than the Air Archon? Is the bonding runestone providing a significant boost to the companion? The tooltip states that it does boost the companion, but not how or how much.