That's like saying Steve Jobs wouldn't be as successful without Jonathan Ive or Tim Cook.
Eisner was a creative and transformative CEO. That served him well. If Wells wouldn't have died, Disney may have been as big as Apple today.
Eisner's strengths were his creative instinct (he wasn't always right, but he had that "this sucks, this doesn't" gut feeling), noticing the little details (let's use the best architects in the world, I want the theme parks to be landmarks) and having big, bold ideas (ABC, ESPN, DisneyQuest, Mickey Mouse Restaurants, Record Label,
Disney Cruise Line, Disney Channel, The Disney Institute, Disney's America, Port Disney, etc.).
He saw no limit for Disney, but he wasn't an implementer—financially or operationally. After Wells, he didn't trust anybody.
He knew Katzenberg was a backstabber (he was) that was after his job. The board was pretty inept (sound familiar?). Roy E Disney was a very nice man, but he missed the boat on 3D animation and he didn't want the blame for the box office flops like Fantasia 2000 or Atlantis.
(Side note: Hilarious people thought these animation masterpieces—Pocahontas, Hercules, Hunchback, Mulan, Lilo & Stitch, Tarzan, Atlantis, Emperor's New Groove, etc—were flops. They were only flops compared to Lion King and Beauty.).
The early 2000's weren't kind to any of Disney's businesses period—thanks to a terrorist attack, major recession and another Gulf War.
Eisner's biggest mistake was Pixar and ticking off Steve Jobs. He didn't appreciate what Pixar had did for the company (again, this isn't surprising considering Pixar wasn't a Disney company and he thought Disney Animation could do it themselves).
After Eisner testified to Congress that Apple was encouraging piracy because of the "Rip. Mix. Burn." commercial, Jobs despised him.
Backstabbing Roy E Disney by forcing the board to enforce the retirement age limit was just icing on the cake.
However, I will say this for Eisner. He may have been complicated, controlling and full of himself, but he lived and bled Disney. You didn't question where his loyalties lie.
I'm not sure you can say that for the current state of Bob Iger.