I think you must compare like to like. Working on a team is always harder since you have to communicate the code you write, and you have to learn the code they write. Teams produce more value as a whole usually, but each individual produce less than if he was working on something on his own.

So comparing how effective you are when you work on your own projects to how effective others are when they work on a large team effort isn't a meaningful comparison. The most valuable programs are all huge collaborative efforts, so even if you as an individual produce less things you typically add more value by working on a big project, while most of the effort people put into their personal project never goes anywhere so ultimately provided 0 value, that is why we put up with teamwork.

But there are many cases where a team of collaborators just never gets anything done. I'm not sure how that happens, but in those cases any decent developer who has practiced some solo projects will easily do it in a fraction of the time. Maybe some developers just never builds their solo development skills and just practice the more lucrative team development skills? But you can't do without those solo dev skills, they are necessary to get out of those deadlocks where a bunch of team players all are waiting for someone else to fix a problem.