I dive solo and I dive in unified teams. As a GUE Tech 2 diver, I can say that the majority of my stress and close calls have been caused by peer pressure from GUE and UTD divers and instructors who put ego ahead of team or who have ignored safe diving practices completely. The advantage to team diving is that you have help and divers are all on the same page regarding procedures. The disadvantage is that buddies can pressure you into diving outside your comfort zone, pressure you into doing stupid stuff, or just go places and do things underwater that puts you at risk or causes you to play cowboy and wrangle the strays back on mission. Worse, you can have three divers none of whom are comfortable with conditions or the psych aspect of a dive continuing just so they don't ruin it for others. No one bothers to communicate and they all assume the others "have got this!"
Solo diving has the advantage of instant self-reflection and communication. You can determine your level of comfort moment by moment and instantly know what you are doing, why you are doing it, and change a dive plan on the fly without confusion. The disadvantage is that you won't have help or back-up brains. If something goes wrong where you can't self-rescue the situation will be fatal.
"Loose team" diving might be more dangerous than unified team diving or solo diving and it is how most of the industry dives. Two or more divers buddy up. They are unfamiliar with each other's gear, training, procedures, and assume they are capable of sharing gas or rescuing a buddy. You have a false sense of security that way and are still subject to peer pressure and possibly endangered by actions of teammates. But, they also may be able to render the help you need and possibly save you.
I started diving solo at age 15 and never got into trouble alone. When I taught solo diving, I tried to get the student to first take an intro to tech class where they would learn precision team diving to appreciate it before going solo. My most recent close call was with a UTD instructor friend in a cave. We had a scooter problem and ended up getting sucked into a siphon 2800 feet back during our return. While working on it, we referenced the guideline quite a bit. Only thing was the line went quickly from our line to another line at some point. We didn't know we were on the wrong line until we tried going home. The scooter I was using was borrowed because my buddy really wanted to scooter that day. I hadn't used that model in a while and a simple switch issue almost became our undoing. Had I been alone, I would have given myself more time to reacquaint myself with the scooter before taking it into a cave.