There’s nothing against any promise there. They create new content for free based on cosmetics, but they never said they’ll stop paid dlc.
This is the first time in the history of vermintide that we have a new career. And weapons being sold as dlc, a new career makes sense as dlc (And this is a pretty big addition in the whole history of vermintide 2). Plus it means that you’ll be actually able to play the character as all players won’t all have access to the career.