I never made claim that Ares is stronger than Hercules based upon their linage just more powerful. More powerful means having more power not stronger. I will concede that Hercules is stronger but not more powerful. In the legends, Ares had a lot of power, more than Hercules. However, in the legends Ares was depicted as the biggest wuss among the gods. With a wound he would go crying to pappa. You can think of him like old Wonderman after he was brought back from his original death sleep. Wonderman was more powerful than only a handful of superheroes but he was a wuss. It wasn't until he regain his confidence that he was a force to be reckon with.
Now let us compare the power of mortal hercules to ares (power not personality or skill)
1. Strength - Hercules (maybe 30 to 50% stronger)
2. Stamina - Ares (Hercules can last for days, Ares can last for months)
3. Durablity - Assume even (although Ares actually greater)
4. Healing - Ares (By orders of magnitude)
5. Other Powers - Ares (He can teleport across dimentions, Olympus, Hades etc...)
If you add up the points for the powers (assuming we assign points to them) Ares is far far more points and more powerful than Hercules.
Now if you ask who would win in a fight that is a different story.
Hercules is a lot braver, and more determine fighter. He is more willing and capable of pushing himself to his limits. His hand to hand skills is second to non among the gods. All of these things make him a better fighter. However, non of those things are power so he is not more powerful. If you want to argue stronger or better fighter I will accept that but not power.
I'll concede most of that to a point, but I'd still contend that Hercules as he has been depicted is sufficiently stronger enough than Ares for Hercules to render most of his brother's advantages moot.