It's not the single SNP, it's the combination of that one with others forming a dynamic. Genetics is a systems science, not a singular causal one. A SNP is a factor, not a cause.
So at best you are left with an infinite number of outside possibilities which essentially reduce the involvement of these CBS SNPs to 0. In which case, it's still not a CBS problem, and certainly not attributable to those specific SNPs.
So I seriously question the motivation of anyone trying to imply someone's experience is not valid because the science is imperfect.
Treatments for sulfur intolerance may produce benefits for a myriad of reasons. There might even be dozens of such reasons which are plausible. But it doesn't make sense to pick a cause which contradicts the scientific research showing that the SNP has a tiny effect, especially when heterozygous.