Hello SteveMacD-- I believe I'm in agreement with you. Although I enjoy Christine's Welch-era music, her songwriting and singing both improved after Linds & Stevie joined the band. Still can't figure out if it's the songs themselves, or the arrangement and production values. But, you can certainly hear the difference, beginning with"Warm Ways" on the White Album. Don't get me wrong, there are some wonderful Christine songs pre-Rumours, but the majority of her best work is clearly during the Buckingham-Nicks time. Just my humble opinion, of course.
Best always, Madelow.