Yes, the irony is that vertically scaling will always go "faster" due to latency until you genuinely need more DB than a single box can handle. Premature horizontal scaling only increase complexity and reduce performance. And even when you genuinely need it the implementation has to fight merely to approach single box latency, which sounds like what these guys have done.

But also vertical scaling seems to be able to handle so much these days that more people probably aught to ask themselves if their application is ever likely to truly need horizontal scaling - Maybe my work is just a small pond, but I suspect we will eventually end up in a place where the vast majority of applications are happy on a single box, and only twitter scale things need to care about this stuff.

.. or maybe I lack imagination of what possible future applications might make use of such massive horizontal scaling on such capable individual boxes (seriously).