I'm a long-time FM fanatic (I met Soda years ago through the FM fandom). Many of us who have listened to the Bob Welch era albums consider some of that work to be some of the best FM ever did.
I'm not discounting the Rumours-era classic lineup but "Mystery To Me" especially could go up against the FM White Album, Mirage or Tango (I'd put it behind Rumours and Tusk) anyday. MTM is cover-to-cover probably my favorite FM album.
Bob is also the reason Fleetwood Mac ever came to California. Mick was open to it but the McVies were resistant. If FM never went to CA, they never would've found Stevie and Lindsey and Rumours never would have happened.
Bob is also what helped FM transition from a British blues band to a UK-US hybrid pop group - another crucial element that led to Stevie and Lindsey.