If it was anything else but gut bacteria, I would be inclined to agree with you, but gut microbiota is slowly turning out to be an extremely important factor in our health and it also turns out that modern highly processed diet tends to damage it and make it less diverse. Even higher frequency of Caesarian section seems to make gut microbiota less diverse and there seem to be some diseases downstream from that.

At the same time, gut microbiota is extremely complex to study.

So, this may be a plausible result. I cannot judge the plausibilities right away in the way you suggest it.