Betaine HCl stomach pH
Betaine HCl is usually delivered in capsules which pass through the mouth and esophagus intact. 
Regarding the webmd article that says " Even if it were true, betaine hydrochloride wouldn’t help. It only delivers hydrochloric acid but does not itself alter stomach acidity."
This statement seems contradictory. Indeed, I found article the tests stomach ph after betaine hcl usage and confirms that indeed it reduces it:
https://www.ncbi.nlm.nih.gov/pubmed/23980906