Well, the issue there is that most of the sources recommending pre-Desert missions without some form of qualifier noting you haven't yet reached the Desert missions are out of date, being from before Dessert missions were brought over. For that matter, while Dragon Hunting did have the best Player XP at the time, it is notably worse than some of the other options for unit XP and most recommendations for it are from before commission sortie, when it was the easiest mission that gave decent fodder and let the player quickly afk while running it (or at least shift over to doing something else). Point is, the Desert maps are generally better for farming than pre-desert maps, and most older players if asked would tell you so.
Technically, in most cases Base Scramble II is the best map to farm for fodder, due to having better drop rates than Fiery Oasis and thus giving more XP per charisma on average, even though it gives worse if you assume perfect drops. In the spoiler here you can find a breakdown of the average unit xp per charisma (factoring in drop rates and with columns for what class unit you are leveling) for the desert maps and the oriental kingdom maps (Eastern Wind seeming to be the official translation). Generally, Fiery Oasis is a good map, but worse than all the desert missions from Base Scramble II and higher (unless you are leveling mages, though one of the Eastern Wind maps will beat it out there).
That said, I agree, it likely is worth updating the FAQ with information on best maps to farm.