Of course Frank Wells was key. They were co-leaders for the first ten years, Wells had just as much power as Eisner, and in some ways he had more. He was the choice to run the company and he was put in a position where he could essentially do so, while Eisner could be satisfied with the title and running the studio. Things generally went well, at least from an external pov. Then Wells died and things deteriorated, and it wasn't just a few things. There was the Ovitz/Pressler debacle. Katzenberg bolted and animation imploded. Relationships with Pixar, the Muppets and others soured.
I am looking at the totality of the regime, and I am evaluating it based on the context of what was going on during the various points in that regime. Without that it's just a surface level analysis.