Jack's greatest sin was transforming a manufacturing company into a financial institute. Similar to a family that takes on debt to appear wealthy it looks good in the short term but the debt always comes due eventually.
It never came due in Jack's time and he looked like an absolute genius. His successor should have been able to defuse the debt bomb over time, but because of the expectations of success that Jack left behind (and some glaring failures of the new CEO) the bomb was left in place and debt continued to pile up.
Of course the bomb went off eventually and the rest is history, GE is not a company anymore.
Aside from the moral issues of Jack's approach (layoffs etc) the true sin is the over financialization of everything in America which I think Jack really set the tone for.
I would highly recommend the book Power Failure with William Cohan. https://www.amazon.ca/Power-Failure-Rise-Fall-American/dp/05...
Lights Out is another great book on the process of financialization that killed GE