Here is the scoop, a majority or probably all the MD's and specialty dr.s like Gastro, optometrist, surgeon etc are not trained or not really introduced to herbal remedies/supplements. Is not what they teach at Med school.
They specialized in their field and follow the general protocols of their field.
There are two or even more approaches to people's illnesses. There is the western, which I assume most of us live in and the Eastern and others somewhere in between.
They both have their pros and cons. In the East, many herbs, treatments are used in conjunction with some western practices. In the west most of our dr are often want to control are symptoms, unless it gets complicated we resort to surgery "in general"
Bottom line is that your Gastro is telling you to follow his treatment.
I personally do take natural supplements and have tried all of those. Some of them help, others did not. DGL, helps me with stomach aches and heartburn. Slippery elm, I tried but it never really helped me. Aloe Vera did help me, but I stopped taking it because I started something different.
Like I said, both medicine schools have pros and cons. It is up to you if you want to try them. Lately some have given natural remedies a bad rap. I think one should investigate themselves before running to conclusions. If western medicine like ppis were the answer to GERD, with no side effects none of us would be here. The same goes for natural supplement, there will not be a silver bullet. Many times is trial and error and both schools have something to offer.