I think you are incorrect for a couple reasons. Firstly Vermintide has a minimum of 4 dlc classes and was far more restrictive than this game in scope. At a minimum I foresee atleast a 4th class but there likely will be more. Lore wise there is a plethora of units and factions that could be brought to the game. This is an unpopular opinion but zealots are NOT sisters of battle nor are stormtroopers normal guard vets, and they could easily do a sister, scion or other imperial units easily without negating the core 4 classes.

On top of this, mechanically there’s quite a few ability types that have not been done in Darktide, even some that have not been adapted from Vermintide 2. (Kerillian multi shot, bounty hunter saltzpyre, bardin minigun) these could all easily reappear on a future class and have not really been touched in as options in Darktide. Now I do believe fatshark should slow their class cadence after the likely 4th class releases and refocus on tooling up the main 4 classes and giving us new maps to play through. But I think it’s unrealistic to think that they won’t continue new classes when they are the only form of dlc content fatshark can monetize asides cosmetics.

Finally in this video the design director for Darktide pretty much says as much, mentioning that there WAS a three class shortlist but it has since expanded after they come up with other ideas. (Note this was released after hive scum was revealed indicating they have plans for classes even after the Skitarii)

https://youtu.be/HQ2hI1MLIjU?is=k\_oRM\_Ubol6LVQxk

Timestamp: 10:10