There can be only one

[FuzzyPlum]

Stevie was such a major draw as part of the live band. She was the undoubted star almost overnight and the main reason the line-up gained traction. She also brought Rhiannon to the table. Would her songs have worked on record without Lindsey bringing them to fruition?
However, Lindsey was such a phenomenal musician. His musicianship was a significant step ahead of what Bob Welch could give them.

Its obviously the combination of the two that gave people the interest. However, I'm going to stick my neck out and say if only one of them had joined it would have been a band featuring Lindsey that would have found more success. He gave them leadership and I think his nous would have found a way to some sort of success irrespective of whether Stevie was part of it or not. Stevie on the other hand was much more naive regarding the business and music in general. Without a musical leader they'd have remained lost.