Mor Dhona is a level 45-50 area though where as Ul'dah is a starting city, hence the Brass Blades low levels. Having said that, the very concept of levels and experience is merely an abstract way of reflecting a character's skill and prowess in fighting (yes yes I know Disciples of the Hand and Land also have levels and exp, but that's essentially the same concept: reflecting a character's ability and skill in a certain area as a numeric value.)

Lore wise, there is no lore basis in levels (except possibly within the Guilds as a means of 'grading' members proficiency in their discipline), so this is definitely an example of gameplay and story segregation, mixed with improbale power discrepancy.