Solo survival is always grueling and the hardships, both physical and psychological, become amplified when you are alone. Humans have survived this long because of culture. We are social animals, so a group would have a far better chance of surviving than the lone individual. For one thing, the more brainpower and braun, the better.
I've done both solo survival outings and group survival trips-where we went out as a small hunter-gatherer bands. These outings ranged up to a month and included very little modern gear. Psychologically, being in a group was far more pleasant and easier, thanks to daily group foraging trips and camaraderie around the evening campfire. We were able to gather more wild food as a group than I ever could have found alone. Simply from a caloric-expenditure perspective, a small group (6-8 people) of trained individuals, in a good environment and at the right time of year, will fare better than the solo survivor.
Yes, many, many people have survived solo. There are countless stories. But loneliness and despair heightened, in my opinion, when you are not able to commiserate with and receive support from others. Recall the Andes survivors. They were a group of young athletes who were already a team when they crashed. Their courage and will to live was fortified by their bonds and mutual support.
Culture is an incredible tool in our survival as a species, so don't vote anyone off your island. That is a bizarre modern concept- our ancestors knew better or we wouldn't be here today!
Your question also brings up the question of whether it is safer to hike with a friend than it is to hike alone. I hike with a friend whenever possible.