Isn't Brettonia the way it is because that's the way that the Wood Elves and The Lady want it? I thought that if they modernized that they would get problems from the Godly front. Or was that just fanon that only showed up in Gaius' quest?
The Nobility isn't allowed to use ranged weapons on Bretonnian soil period.
That means most knights don't use gunpowder.
The Doomsphere on the other hand. is Melee(and thus perfectly legal).
Bretonnia's navy technically isn't on Bretonnian soil though, so they have no such restrictions.
Also, IIRC peasants weren't allowed to worship the Lady(who forbids the use of ranged weaponry) so they also don't have said restrictions.
Otherwise, why would the 6th edition Bretonnian army book have peasant bowmen(page 53) and field trebuchets(page 56)?