The protagonist of Tales of the Abyss is the son of a duke. Although they refer to his father as such, their retainers refer to his mother "lady" and he himself "young master." From my small amount of Japanese, I gathered they probably were called 様 and 坊ちゃん, and that would be a good translation. It's just in English that makes no sense. The wife of a duke is a duchess. And their son is a lord. Well, OK, the eldest son is usually given a lesser title like viscount (which the protagonist received later in the game) or marquess, but even the younger sons would be called a lord.

Based off of Great Britain, which is where English originated and still has all these positions, this is how it goes:
King/Queen: Your Majesty
Prince/Princess: Your Highness
Duke/Duchess: Your Grace, Your Excellency
Earl/Countess: Your lordship/ladyship / My lord/lady
Marquess/Marchioness: Your lordship/ladyship / My lord/lady
Baron/Baroness: Your lordship/ladyship / My lord/lady

("Your Excellency" and "Your Grace" are admittedly a mess. Usually those are left for diplomats, certain members of the royal family, heads of state, archibishops and bishops, and other high-level positions in government. It changes depending on the country or religion.)

It's literal translation vs. English usage. For video games we have two levels going on here: I'm just gonna assume most Japanese translators in that position don't really know methods of address and styles because it's not their area of interest. But simultaneously I'm also gonna assume Japanese doesn't either. Oftentimes they create a story that feels western -- the protagonist's home in Abyss definitely would be more appropriate in a European context than a Japanese -- but they still have to work within the honorifics that originated within their own language. It's a difficult situation to put the translator in. But I still feel if you're going to translate one dude as "duke," you gotta make it work for his entire family. If he's a duke, why isn't his wife a duchess?