In that case, if these hearings aren't part of the congressional mandate of the DEA, why was it necessary for John Lawn to, as widely quoted by the DEA, in court, reverse Young's ruling? If these hearings weren't intended by the congress to carry some sort of weight, why do we bother with them? The legality of the DEA's actions are, in fact, questionable, and that's why they're being questioned in court.
John Lawn rejected (not reversed) Francis Young's recommendation (not ruling) on the grounds that there had been no extensive large-scale controlled studies to demonstrate the effectiveness of medical marijuana.
"If these hearings weren't intended by the congress to carry some sort of weight, why do we bother with them?"
These were not Congressional hearings. It was ALJ Francis Young presiding over a hearing attended by a group of 9 people representing various interests presenting their data to the U.S. DOJ/DEA.
The ALJ received this data in the hearing, typed it up, and submitted a 69-page report, along with his recommendation, to the DEA. The DEA looked it over and rejected it.
I bet this happens all over Washington 100 times a day by various interest groups petitioning various government agencies.