One thing about this thread is that it seems to be comparing the best of school experiences with the worst of homeschooling experiences, which seems a bit lopsided. Yes, some schools are awesome, wonderful, no bullying, enthusiastic teachers, small classes, great opportunities, and can provide things that homeschooling can't. But not everyone has access to a school like that. In fact, I would say most people who homeschool don't have access to a school like that, since I would guess that most public schools aren't like that and many people who homeschool can't afford private school. Of course all public schools aren't horrible and some are better than others of course. But, the really "awesome" schools seem to be mostly private.
And of course, homeschooling can be a bad experience with burnt-out parents, isolated kids, etc...so it goes both ways.
I had a pretty typical public school experiences. Decent school district in the middle of typical suburban school in the Northeast. Most students were from white collar families. Some years I had good teachers, other years not so good. Some years I experienced more teasing than others (I wouldn't say I was ever really bullied, but I was teased a lot and didn't have many friends). It was a decent school dist4rict and probably even better than average. I was a good student and highly self-motivated so that made a big difference for me. I woudlnt' say I had a bad school experience, I would just say it was "ok"
Regarding group work and collaboration, I did way more beneficial group work through 4-H (which I was very active in) than I ever did in school. In 4-H I was on leadership teams, and put projects together. It was a wonderful experience. We did do group work in middle and high school, but it always felt like *I* as a good student was pulling along the less than good students. Or I was the one teaching the concepts to the people who didn't understand it. I think the value of group work gets muddled a lot when grades are involved. Grades only motivate *some* students, so then you basically get the students who are motivated by good grades working harder and the students who aren't just coasting. With 4-H, my group work wasn't motivated by grades, but rather by a common interest or project, so it was much more beneficial.
Really I think what it boils down to is that a school experience could be good, bad or average and a homeschool experience could be good, bad or average. The major difference is that as a parent, I have a lot more control over my child's homeschool experience than I would over their school experience. If I decide my child needs more group work, I can find ways to do that (coops, classes, starting a group, working with siblings, etc.). It's a lot harder to say "hey, Mrs. Teacher, I think you should do x,y, and z in your classroom". Or, if I decide that math curriculum we are using isn't working I can change, while if I decide the math curriculum the school is using isn't best for my child, I probably can't do anything about it. I can make suggestions, but oftentimes curriculum is district-wide and outside the control of parents. Of course, there are things homeschool parents may not be able to offer (due to time or expense, etc.) but then there are a lot of homeschool experiences my child has had (ie. ice skating, dissecting a shark, swimming lessons, etc.) that I never had in public school.