Let's see if I understand this correctly. He's saying that Vanguard's low-cost structure and the trend towards buy and hold investing has changed the way professional money managers work, slowly moving them away from the active churning of funds which used to generate commissions.
And this is somehow a bad thing? Is he worried about a market in which brokers don't profit by buying and selling for no reason? His observational support is that the market keeps climbing, with the dips being bought in short order instead of drawing out for months and months of decline, and he thinks it is because too many people have money to invest.
This looks to me like a period of rising prosperity, not an alarm bell. I don't see how his interpretation generates any actionable advice. What strategy would you adopt if he's actually spot on? What would you do if he's got it all wrong?
It just seems like half of an article. He offers his opinion about why the market has done so well, but then he doesn't take that next analytical step to tell us what that means. Is it supposed to be obvious and I'm just no seeing it? If the US economy is chugging along so well that vast sums of wealth are being generated and invested in businesses, isn't that best strategy to ride that wave? Don't most investors fantasize about prolonged periods of steadily growing economic activity and corresponding equity valuations?
Or maybe he's sore about this because he was one of those day traders who's been shorting every bump for the past two years? We have several folks like that here on this forum, people who said the market was frothy 18 months ago and they were 100% cash until the "inevitable" coming crash that they were sure was just around the corner. I can see how somebody like that would write this article because they're upset about the rising tide.