I think that it's like anything in life. "It depends ...." Contrary to what my forum name implies, I'm not really a loner. One of my favorite things to do is day hike with my wife. It's terrific quality time together. Other times I'm perfectly content to go off alone while she has dinner with her sisters.
I personally believe that if you are well prepared, you are just as safe alone as you are with a group and in some ways, maybe a little bit safer. We make preparations as best as we can but you just can't cover every contingency. Accidents do happen. It's kind of the price we pay for doing the things outdoors that we do.
One thing to keep in mind, and this is probably not too much of an issue in here, but I've been on hikes with a group and one of the group is a much stronger hiker. They tend to want to push the pace and if the weaker ones try to keep up, it can cause someone to go past their own personal safe limits and get hurt. I have seen that happen.
LW