If it were true wouldn't all democratic societies be in danger. Our whole society is based off the wisdom of the crowds.
I agree with the overall conclusion, even if it's phrased misleadingly: human collective intelligence is primarily about individual intelligences accessing group knowledge rather than groups working together to tackle complex problems beyond individual comprehension. Ants are not individually capable of understanding the piano-mover problem at a basic level; research administrators are generally capable of understanding the work of individual researchers, they just don't have the time to digest all the details.
Democracy is more or less in a permanent state of crisis. This has been discussed thoroughly since the time of Athens, and certainly Rome. The late days of the republic were characterized by squabbling over the specifics of who got to lobby voters, how they were allowed to, and where they were allowed to. For instance they have laws on the books dictating the physical structure of the buildings that people voted in to ensure that the rich couldn't basically station people in the halls leading to the ballots to purchase votes or physically intimidate voters. This is also reflected in the sudden populist turns of eg the Gracchi brothers and Caesar himself.
It's also true of the American republic. Self-conception of us as an egalitarian democracy is still around at best a century old, and more accurately around sixty years old. And we remain extremely far from being an obviously healthy democracy. Of course, the state has vacillated between actions you could argue are wise and those that are clearly not, before and after these divides.
I really would be very cautious at viewing democracies as reflecting of "wisdom". We often can (and often do) come to consensus that is extremely ill-advised from the perspective of the needs of the populace. Democracy is more or less permanently perched on the tension between the will and needs of the constituents which are often at blatant odds with each other. There's a reason why the Philosopher King has held such a cultural weight through the millennia. At best democracy is a best-faith effort to approximate wisdom through consensus—sometimes with better faith than other times.
Maybe we should define democracy and state of crisis before reaching to any conclusion.
We can just as well consider human history as a graph of political crisis.
As for democracy, if we mean a system were everyone in the crowd is equal citizen and the people officially rules itself directly, there is probably no single State in the world that fits the definition.
Sociopaths have an edge to rule society as they are inclined to impose their agenda through relentless use of all the means they can think of while most people will refrain themselves from most crual actions for ethical concerns.
And of course sociopaths are going to pretend they became and remain king thanks to the will of some mighty divinity, their demiurgic actions, and their exceptional wisdom.
The appealing point for democracy is that those who have to follow the law are those who makes the law, do a feedback loop can tweak the way the society organize along the way without possibility to ignore the actual consequences of these decisions.
Something like estimating the number of beans in a jar is a good fit, since there is only one layer of perception to agree on and no coordination required.
This experiment as described seems closer to “design by committee” with (predictably) similar results.
All democratic societies are in danger -- because the wisdom of the crowd does not have the capability to handle scenarios where the crowd has sufficiently great power.
Nevertheless at the end of the day we will have political systems anyway.
In that case, the text was specifically pointing to how so general statements can hardly lead to any robust conclusion.
All systems have their unique weaknesses, which can lead to dangerous situations.
On a pure retorical level, we can pick any system that can be conceptually exposed and discuss its theoretical virtues all day through. Or expose all the danger we can envision from mechanisms it implies on conceptual level.
In theory, an enlightened dictator is the best system, just as well as democracy with enlightened crowd, or gerontocracy with enlightened elders that don't fall in illusion that everything was better before and new generations are a bunch of lazy arrogant ignorants that will doom the civilization, or whatever gouvernement form we can theorize about.
It's easy to blame the ruler when you are not put with the duty to actively participate in the policy creation that should content all stake holders, and it's easy to blame the ruled ones when you don't have to obey the same rules as everyone because of course your exceptional contributions to society necessarily implies exceptional privilegies and you are the one that makes the laws anyway.
Except of course in a system where everyone is imposed the duty and means to contribute to maintain and evolve the laws that everyone have to follow, self included.