I would attribute Google+'s failures much more to their abysmal launch strategy, which massively restricted otherwise-excited users from ever joining Google+ until it became a barren wasteland.
The end result was every article about Google+ carried with it some form of controversy, negativity or problem. Joe average might not care about the real name policy at first, but they do care when they're told it's broken, sexist, racist and dangerous.
I'm not saying the real name policy didn't hurt Google+. I'm sure it did, but I think it could have weathered that storm if it wasn't weak in much more important areas like their launch strategy.
Or worth being influenced by…
Forcing me to use real name means that I suddenly must be super careful about everything and control everything the same way as I control work. Not worth it.
On the other end my siblings, cousins, school friends and some more all kept their AOL/hotmail/yahoo mail or other chat service nickname, which for a reason or another was a nickname.
I think it really depends on how, when and for what someone first came to the internet. If it was for fart jokes, or activism, real name policy is a bummer.
I don't think that anyone will argue that pseudonyms are important to the average user. However, they are important to a small but influential group of users. The type of early adopter that otherwise could've driven G+ upward.