Hawks and falcons don't defensively "drive off" Great Horned Owls during the day, they aggressively attack and try to kill them -- given the opportunity, which they rarely get, as Great Horned Owls are excellent daytime hiders for that very reason.
That is why hawk/falcon banders use plastic dummies of Great Horned Owls for catching many species of raptors, particularly during migration. The raptor thinks it sees a bird it hates, in the open and vulnerable during the day, and it will come from great distance to attack at full speed -- only the banders get them with a net first. When you look at banding statistics, accipiters and falcons are the most enthusiastic about attacking owls, while larger buteos like red-tailed hawks regularly give it a try, and it is rare for eagles to bother.
It is not a matter of one bird being "tougher" than the other, all five kinds I mentioned are superb killers, and it is not like they are duking it out in a boxing ring on equal terms. The bird that is making the surprise attack is the one with the huge advantage. That tends to be owls at night and raptors during the day, though there are some diurnal owls that can hold their own, such as Great Gray Owls and Northern Hawk Owls.