It may have been a windfall to other companies outside the conspiracy but it was not a windfall for the employees of those companies. Collusion meant the big companies didn't mean to pay as much as they otherwise would have. This means smaller companies can also pay less for the same talent. I worked at one of those smaller companies in the Bay Area. I have every reason to believe that if market rates were higher I would have received more pay. I do not consider myself a beneficiary of this scheme.
But if the employees were truly worth more – they produced more in value – then as long as new companies were free to start (some indeed started by those same ex-cartel employees themselves), then someone would pay that full value.
And if, with hundreds or thousands of potential employers, almost all outside the cartel, the salaries were still what they were... then what's the proof employees were worth more, anyway?
If there's some purchasable commodity that can generate $X in value, then a competitive market will tend to offer up to ($X - epsilon) for that commodity. Even if a cartel of a few of the biggest purchasers A, B, and C coordinate such that they'll only pay (0.90 * $X), the existence of dozens or hundreds or even thousands of other self-motivated bidders mean the commodity is still going to go for ($X - epsilon).
The same goes for skilled labor. The A, B, and C cartel may be driving down their short-term compensation costs a little, but by incrementally letting talent that's more productive go elsewhere, that talent and the economy is still doing just fine.
