Stephen Squeri appeared to check all the boxes as the next CEO of American Express. By 2016 he had spent three decades at the credit card colossus, reshaped tech operations, headed the corporate and merchant franchises, and orchestrated a spectacularly successful restructuring. But the Queens, N.Y., native had a giant liability in his quest to succeed the crisply tailored, cuff-link-sporting Ken Chenault: He didn’t dress like a Wall Street CEO. …