I only read page one of that link (thanks for sharing), but it appears to limit its scope to a specific scenario: given a lump sump of money (a windfall), it is it better to invest all at once or dollar cost average over a period of time? It is not recommending against dollar cost averaging in general; it is recommending against it for windfalls. Diversification is also not mentioned in the article.
I read that Vanguard study when it came out, yes it's correct statistically but I disagree with using that data to do lump sum investments. For one, the CEO in their 2018 outlook webcast said to DCA. Even if you keep a short timespan on your DCA (I do 26 weeks), it's a good idea for your mental health if you happen to dump it all right before a collapse.
Sometimes it's wiser to take into account human psychology, even if academics are out there with data to convince us otherwise.
I'm personally with the CEO of Vanguard on this one. A short entrance into the market, especially in today's situation is probably the way to go. People can do whatever they want, and if they put their money where their mouth is and go in with a lump sum, then I'll respect it.
Otherwise, as someone who is bringing a lot of money myself onto the market now, I'm DCAing.
