For Fortune magazine in 1999, Jack Welch, then General Electric's chief executive, wasn't just the country's best executive, or the manager of the year, but nothing less than the best manager of the 20th century, "far and away the most influential manager of his generation."

Mr. Welch himself was more circumspect. "My success will be determined by how well my successor grows it in the next 20 years," he said at a management conference that year.

Eighteen years later, with this week's announcement that Mr. Welch's handpicked successor, Jeffrey R. Immelt, would step down as G.E.'s chief executive, the verdict would appear to be in.

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"Given how horrendous the stock performance has been for so many years, the most amazing thing is why the board didn't act sooner" to replace Mr. Immelt, said Charles M. Elson, a professor and director of the John L. Weinberg Center for Corporate Governance at the University of Delaware.

Scott Davis, a Barclays managing director, said on CNBC that Mr. Immelt's tenure was "an unmitigated disaster for shareholders."

Mr. Welch brought much needed energy and charisma to the chief executive's job and streamlined G.E.'s bloated bureaucracy. Had he stayed on through the financial crisis, perhaps he would have recaptured the growth that eluded Mr. Immelt.

But hardly anyone considers Mr. Welch, now 81, a management role model anymore, and the conglomerate model he championed at G.E. — that with strict discipline, you could successfully manage any business as long as your market share was first or second — has been thoroughly discredited, at least in the United States.

No wonder, given the performance of the company's stock over the past 10 years. G.E. shares dropped 25 percent during that period, in contrast with a 59 percent rise for the S.&P. 500. The rival industrial conglomerate Honeywell's stock has more than doubled, and Danaher's has tripled. United Technologies gained 67 percent.

Nonetheless, Mr. Immelt remained one of the country's highest-paid executives: $21.3 million in 2016, $33 million in 2015, and $37 million in 2014. Even without a formal severance package, Mr. Immelt, 61, will get an additional $211 million when he retires, Fortune estimates.

"I'm a long-term G.E. shareholder," Mr. Elson said. "The bottom line is, I did poorly and he did very well."

Speaking of his tenure as G.E.'s leader, Mr. Immelt pointed to the increased strength of the company's industrial businesses, their competitiveness and large market shares.

"I'll say that will stand the test of time," he said in an interview on Monday with my colleague Steve Lohr. "Let other people make their own judgments."

Mr. Immelt's defenders have pointed out that he had to contend with the collapse of the tech bubble, the Sept. 11 attacks and the financial crisis, all circumstances beyond his control. But so did the chief executives of every other major company.

"About the best that can be said is that he enabled G.E. to survive through a difficult time," said Bruce Greenwald, professor of finance and asset management at Columbia. "But he never really understood how to create value through growth."

And he inherited "a highly inflated stock price," Mr. Greenwald said, thanks to Mr. Welch's aura and lofty expectations that probably no one could have met.