It's confirmed that the Belmonts became vampire hunters not too long after Leon's struggle, not "generations after cuz they lose interest." The PoR timeline states that they kept busy hunting down various vampire lords, each one they slayed added to Dracula's power. IGA is also on record saying that "if he were to shed light on this period, it would be more about, how did the Belmonts manage to track Mathias for so long? Being vampire hunters doesn't just mean Dracula, so who else were they hunting?"
So for someone to say there's nothing more they can do game-wise between LoI & CV3 is "utter bullshit." People will buy them as long as the gameplay's good.
"b-but it's called Akumajo DRACULA!"
Dracula can still be featured without him being killed/fought. Also, they can make a reverse-AoS that showcases how Mathias gained allegiance from all those monsters he controls.