Conversation so far:
When did Welch join Fleetwood Mac?
1971, when he was invited to join Fleetwood Mac.
What was his role with Fleetwood Mac?
Welch helped to steer the band in a more melodic direction, particularly after lead guitarist/singer-songwriter Danny Kirwan was fired.

Question: Was Welch successful?
Self-contained rewrite: Was Welch, from Fleetwood Mac, successful?