I completely agree with you, but don't forget one other hugely important decision wrt to G+ that was controversial at the time: the refusal to release a full fledge API. To this day, the only real client for Google+ is the one made by Google. We've all come to accept it at this point, but back then Google was a company entirely built around the concept of APIs for all their services. No matter what the service, you could integrate with it. G+ was really the first time ever that they said "no, API for you".

Had Google skated around the identity issue AND enabled an ecosystem of 3rd party APIs similar to how Twitter developed, I think G+ would own the entire social network ecosystem by now. Instead, they've got a small piece of the pie, which some will claim is more valuable because it is full of "real identities" and completely controlled by Google, but to my mind is far less value because it intersects only a tiny cross section of society who use it.