While I fully agree with your first statement, I don't think the rest follow.
Sergei and Larry (possibly mistakenly) felt like they wanted to rebrand Google as a "social network that manages all information you could ever want," as opposed to a "web search engine that also provides email, messaging, picture sharing, and a bunch of other random stuff." If you look at it that way, rather than forcing everyone into a social network, they were trying to pull everything else they offered underneath their G+ umbrella -- Imagine if FB started out as say, just messaging. Then offered "friending," basically to the extent of LinkedIn - see job info, school, etc. Then offered photo albums. And then one day said "oh all this goes into your facebook profile, we're a social network now." The end product would be the same as what we have today.
Would we would probably all be shoveling the shit onto them too? Probably. But that doesn't inherently make "facebook" a terrible product, or the idea of tying all those services into a single social network "insane," I don't think.
I think from a meeting-room/white-boarding level, what google was trying makes a LOT of sense. It makes Google's offerings more cohesive. That it doesn't happen to be the way YOU as a customer sees or wants to see Google was not considered (and that's their failure). They seemed to just be running on the vision of what the end product would look like, which would be a competitor for Facebook, but with VERY different, several unrivaled sub-offerings. Turns out they forgot that how they get there matters a lot too.
I also think they were on the pathway to innovating further, starting with Hangouts...no other social network where nearly all your friends were gave you multi-way voice+video chat, sharing the same YT video, etc. I think they could have done more, but G+ just sucked so much that it could probably never get any of its labs features off the ground.
I hate G+ as much as the next guy, and especially hate how Google tried to shoehorn such a bad product into every google user's lives. But that doesn't mean their vision was nonsensical. It was probably a bit of tunnel-vision though, and it unfortunately did not take their existing userbase's sensitivities into account. Oh well.