Simply stated, you're probably right. There IS an advantage. However, depending on environment, experience, and equipment, I'd say the advantage can be very slight. Which is why man folks say "the heck with it." Going with a partner, for marginal benefits, may be outweighed by factors such as route, timing of the excursion (I'm off this weekend, you're not, I'm going!), etc

I've gone hiking solo. A few overnighters solo. But honestly, I appreciate the company of 1 or 2 others. It's not a thought-out, "safety" issue as much as it is, carry less weight, someone to talk to, easier to get camp set up, etc.