The enduring strength is it is private and can keep itself well hidden from the public, regulators and employees. There are Wells Fargo like scandals that could be made public that would tarnish the companies name, but the firm does a great job at managing that risk.
And "back in the day" Ned appreciated and cultivated an environment that reward an honest effort: not saying it was perfect back then, as many a sleaze bag climbed the ladder, but still if you worked with integrity it also got recognized/rewarded. Whereas today if you are of an ethical mindset you are the main attraction at the carnival.
Further when internet bubble imploded and exposed the real profit centers the whole "Scale" idea began to get implemented and the slow decline into a Walmart like business mind set began. Plus the market competition arising from the shift to internet based low cost alternatives; Fido always being behind on innovation, forced the rush to lower the standard.
Mirroring the scale approach is highlighted in personnel, a high school diploma will get you a phone rep/branch rep job. Last year you were at prom, now you are a financial professional.
Fidelity is purposefully insulated/hidden from the world, turn on CNBC/Bloomberg and when they highlight an upcoming business round table with CEO/Leaders from financial companies you will never see Abby sitting along side any of those folks, The place is invisible, maybe this is its strength!