If that is true, and there may be a point, you might want to consider what the specific evolutionary benefit mechanism of that swarming behaviour is, and what its costs are.

In the case of passenger pigeons (now extinct) and locusts (not a species but a behavioural mode of specific species of grasshoppers), the swarming behaviour was a mobile one, essentially a fast-cycle nomadic activity. Swarming for each both provided defence against predation (any predator species were overwhelmed by the number of prey) and against competition: by moving rapidly across landscapes, passenger pigeons and locusts could out-compete other species for food sources (including humans).

If there's a benefit to human-based swarming, it doesn't appear to follow either of these modes. Humans don't swarm in mobs (outside of riots, and there, for similar advantage), but in stationary urbanisations. And the benefits seem to largely be of information flows and interactivity or interdependence.

At the same time, cities have multiple vulnerabilities. They aren't mobile, they require prodigious resources (Los Angeles, as an example, sources water from up to 1,500 miles away, and every city on the planet is dependent on oil which is found in only a few specific high-concentration regions and much of which crosses oceans to arrive), and of waste removal.

So, yes, humans become more effective competitors as they aggregate. Until, perhaps, they don't.

Fly in the ointment and all that.