nogrammer
Come on, now - understanding natural language is pretty much the 0 yard line when it comes to AGI, the fact that it's not solved now doesn't tell us anything about how far away it is.
And I'd be on the lookout for massive advances in NLP over the next couple of years; there have been enormous leaps in 2018 alone when it comes to how good we are at understanding text (better applications of transformer models, high quality pre-trained base models, etc.), and now that there have been a few high-profile successes we're likely to see that field evolve just like computer vision has, even though I grant that it's a much harder problem in general.
G+ positioned itself against Facebook sort of like DuckDuckGo went against Google: we made the same product, but fixed X!!!, where X is some gripe about the incumbent's product that only a small percentage of the product's potential userbase cares about (privacy, in both of these cases).
That was (and is!) a fantastic strategy for DDG, for whom a fraction of a percent of all search traffic counts as massive, life-changing success. Google is not DDG, though. G+ would have needed a much larger share of the social networking market to be considered a win for Google, and the initial differentiation was not anywhere near clear enough to get there against a rival as strong as Facebook.
I also agree about the UI mess, and all that, of course, it was not a great product to use out of the gate.
This article outlines some great first things to look for, but something important is missing: sometimes, after trying everything, it turns out that your team just has some truly terrible, morale-sucking people on it, and they need to be fired before things will pick up. That's sort of the "file a compiler bug" option of last resort, but there really are a lot of toxic people like that out there, especially amongst programmers, and as a manager you'll need to be able to pick them out and deal with them. That's almost the most important part of your job.