So, Half-Giant Barbarian with Large +1 flaming greatsword, permanently Enlarged and with +4 Str Belt, while raging:Weapon + str + magic + flaming + Power Attack + Vital Strike
4d6 + 13 + 1 + 1d6 + 6 + 4d6
9d6 + 20, Minimum 29, Average 51, Maximum 74
Attack Bonus: +7 BaB +9 Str +1 Magic -1 Large = +16
Feats used: Power Attack and Vital Strike
As you see, an average of 14 damage (around... 25% of total? my math is iffy) is coming from Vital Strike alone. That's not a problem with the Aegis.
Actually the problem here comes from the gear. I made the Ageis assuming level 7, which is a budget of 23.5k in gold.
The +4 strength belt is 16k.
The +1 Flaming Great sword is 18k
Putting you at a minimum gear budget before any other items of 34k.
The Ageis did that with the 23.5k with 5.5k gold remaining, and he had armor as well.
Also, how are you getting your +13 to strength mod? An 18 (+4) is a +6 with a 2 handed weapon. Raging you will get to 22 (+6) which will be a +9 with 2h. Enlarged will pump it to a (+7) bringing you to a +10 2h. Keeping in mind that I didn't factor in the 4th level stat boost into my build, I'm just not sure how you are coming up with your +13. Or do you assume that you are starting with a 20 str at level 1?