If we were talking about fad diets I might agree with you and your GI doctor. However we are talking about clinical trials of probiotics like the one done on Align by Prof Peter Whorwell director of the South Manchester Functional Bowel Service in the UK. He is the GI doc who developed the gut-directed hypnotherapy for IBS in 1984. He was the first to claim insoluble fiber can be problematic for IBSers and his group examined the role of food intolerances in IBS. I believe some of his findings, particularly the role of IF and SF and hypnotherapy, have informed Heather about her approach to managing IBS. He is a GI doctor with credentials - I expect even your GI doc knows about his work.
It is important to keep IBS triggers in perspective. A minuscule amount of dairy in a probiotic is quite unlikely to cause problems for most IBS suffers. If the researchers in Manchester, who are fully aware of the problems of IBS and diary, were worried about the small amount of casein in Align they would not have used it in the clinical trials.
However, if you feel small amounts of dairy derived products are a problem for you then by all means avoid them
-------------------- STABLE: ♂, IBS-D 50+ years - Science of IBS