I've heard of this desensitization stuff before too. For all the mixed reviews of it, maybe success simply depends on individual factors that nobody has identified yet.
Yes, this is known to be true. Studies of oral immunotherapy often show failure rates in the 20-30% range, and nobody knows a way to accurately predict who will succeed and who will fail without actually going through the whole treatment. IgE levels can correlate with success but they are far from a perfect predictor. The other big factor is age. If you can start immunotherapy super early, like in the 0-2 year old range, it is significantly more likely to work.