“To the extent that you have seen innovation by insurers, it’s often at the behest of employers,” said Jonathan Kolstad, an associate professor at the University of California, Berkeley, who studies the industry.

The announcement on Tuesday by Amazon, Chase and Berkshire, though short on details, generated a lot of hope and investor enthusiasm. There are reasons to be skeptical that the companies will be able to make a big dent in their workers’ health spending. But if the companies succeed, they will be harnessing the advantages and opportunities of a much maligned part of American health care.

Companies started offering health coverage broadly during World War II, when the government imposed wage controls. And the system was cemented when the Internal Revenue Service decided that health insurance was not subject to income taxes, making it a particularly valuable way for employers to improve compensation for their workers.

Critics point to numerous problems with the system: It relies on company leaders to pick health insurance for all workers, even though C-suite executives might have preferences different from their lower-wage employees. It diminishes incentives to reduce costs, by insulating workers from the full price of their benefits. It discourages changes that could displease even a small number of workers, creating incentives to minimize disruption. “I don’t see any reason for the employer to be doing this,” said Fiona Scott Morton, a health economist at the Yale School of Management.

But the employer system also has points in its favor. For one, proponents note employers have multiple incentives to get health insurance right. They want their workers to be happy with their full slate of compensation — an employer that offered deceptive plans, for instance, might not hold onto good employees for long. Employers also want workers who are healthy and productive, able to work hard and to focus on their work.