1) It is generally accepted that the best people leave first in this kind of layoff. But 3 years later, the corporation is doing as well as the others. Hence, removing the best people does no damage to a bigcorp.
2) A post in this thread describes how regular aggressive layoffs turn the culture toxic, setting people against each other. But one common response in nature is cooperation: people form a clique, and exclude colleagues who could damage them. They make nonmembers perform badly by e.g. witholding information. This sers outsiders up for being laid off. An evolutionary pressure selects for people having the political prowess to survive layoffs, and against good performers which endanger the status quo.
So a bigco's level of performance does not depend on having good workers. Instead, all this points to the work performed by the worst workers to be the major determinating factor for success.