I think Dropbox is a great example to illustrate the weaknesses of the product-to-feature template. Yes, a product can be crushed by a feature, but only if that feature is "good enough".
Dropbox, in particular, is remarkably resilient, because the competing features still aren't "good enough". Apple and Microsoft are actually relatively weak competitors because neither of them "plays well with others" (and having access to your files "anywhere" is a big part of Dropbox's value proposition). Amazon is a more significant threat (competing with your infrastructure provider is never easy), but even they haven't done enough to make Cloud Drive simple and ubiquitous.
Looking at Google+ that way, I think many products won't be threatened by Google+'s features. For example, Google+ doesn't support anonymity the way Tumblr does, so it isn't likely to be a "good enough" replacement.
Facebook might be special case, though. Other than the existing user base (which isn't an impossible hurdle), I don't really see any dimension along which Google+ isn't likely to be a "good enough" alternative. On the other hand, I've never been a fan of Facebook, so I'm probably a bad person to assess that.
People are invested in Facebook with their updates, photos etc. Unlike what the OP contends, people are not going to switch over their usage to a competitor based on features. Bing is as good as Google for most queries, but how many people have switched to Bing? Google is not attacking, it is defending. FB messages is already way more efficient for quick communication than email. It may not replace email, but can occupy significant market-share.
No matter how many places Google pushes G+, people are not going to switch unless they can achieve the same functionality by copy-pasting a link.
People were invested in Myspace with updates, photos, page customizations, etc. Now they're all on Facebook. There's no reason to believe they won't move again if the right feature set comes along.
I'd actually expect that Facebook's far deeper penetration would mean that there is a far lower percentage that are willing to jump on the "next big thing".
While I agree that Google+ has any advantages over Facebook, a lot of users just use Facebook as a way to quickly share information and be done with it. While Google+ has many good features, it does not pose a good enough reason to migrate to a new social network and build up there entire network again. I understand this is a major generalization about Facebook users, but I think it's fine in this case.
Ironically enough, Facebook effectively support anonymity more than Google+ and that will keep a significant number of people off of Google+.
Consider, however dubious I might find Facebook, the only thing that I would move to is something like what diaspora promised - a less corporate, more anonymous platform. I won't move to Google+ no matter and so some number of my friends won't find me there ever. A small number of my friend have talked about moving to G+ yet are still on Facebook. I suspect this dynamic will protect Facebook until something offering a more desirable platform comes along - G+ calling itself an "identity platform" seems to scream that Google will be selling its members even more than Facebook sells us.
Dropbox, in particular, is remarkably resilient, because the competing features still aren't "good enough". Apple and Microsoft are actually relatively weak competitors because neither of them "plays well with others" (and having access to your files "anywhere" is a big part of Dropbox's value proposition). Amazon is a more significant threat (competing with your infrastructure provider is never easy), but even they haven't done enough to make Cloud Drive simple and ubiquitous.
Looking at Google+ that way, I think many products won't be threatened by Google+'s features. For example, Google+ doesn't support anonymity the way Tumblr does, so it isn't likely to be a "good enough" replacement.
Facebook might be special case, though. Other than the existing user base (which isn't an impossible hurdle), I don't really see any dimension along which Google+ isn't likely to be a "good enough" alternative. On the other hand, I've never been a fan of Facebook, so I'm probably a bad person to assess that.