You could always ignore the ESO Khajit lore. And by Feral I mean...Feral. The Senche cannot speak, and since other races can go feral too, I don't see why the Senches in that region couldn't. About the Mane...I agree that they may have messed up.
As for the slavery, that is incorrect. When the Pact was formed, The Tribunal made the Dunmer release the Argonian slaves, so they took Khajit slaves instead. (And other races, such as Goblins)
The bad blood between them is constantly referenced, and Blackmarsh is full of illegal slavers capturing Argonians, and there are several quests with vengeful Argonians trying to murder former Dunmeri slavers.
The Xanmeer are the old Argonian ruins from the time when their civilization was more advanced.
In fact you meet some of the advanced Argonians who built those structures later on.
As for the slavery, that is incorrect. When the Pact was formed, The Tribunal made the Dunmer release the Argonian slaves, so they took Khajit slaves instead. (And other races, such as Goblins)
The bad blood between them is constantly referenced, and Blackmarsh is full of illegal slavers capturing Argonians, and there are several quests with vengeful Argonians trying to murder former Dunmeri slavers.
The Xanmeer are the old Argonian ruins from the time when their civilization was more advanced.
In fact you meet some of the advanced Argonians who built those structures later on.