I'm not sure about that. They were very much still a cohesive unit when Return of Saturn dropped in '99 though the signs were there. By the time Rocksteady came in '01, they were definatley "The Gwen Show co-starring...".
Gwen's romance with Gavin Rossdale didn't help things.
I'm blaming her upsurge on the decline of the band. Rings Of Saturn just didn't feel right to me. Rocksteady is straight up bad and might as well be the first Gwen solo album, anyway.