It is kinda difficult squeezing fresh content out of Dracula all the time.
Dracula rises and causes trouble.
Belmont rise to the challenge, despite bad public relations.
Belmont slays Dracula, Belmont is either regarded a hero, or no one cares.
Hundred or so years later, Dracula resurrects, rinse and repeat.
I know Dracula is a public domain villain, but why not let some other great evil challenge the Belmonts every now and again?
What about, a London adventure that still has a vampire overlord, only instead of a grand castle and an army of monsters, this vampire is Lord Ruthven. He claims to be older, more powerful than Dracula, only instead of sitting high in a castle, he walks amongst the aristocracy and manipulates them into his bidding. Thus the Belmont can't just whip his way through monsters to get to Ruthven.
Or, for the sake of traditional gameplay, perhaps Lord Ruthven set up his base of operations in the famous Catacombs of Paris, turning the catacombs into an extended dungeon-underground fortress like place.
Did you know that the franchise originally isn't known as Castlevania and that's still the case in Japan?
In Japan, the games never uses Castlevania name, they're known as
Akumajō Dracula series.
For example the game we knew as Castlevania: Rondo of Blood was released in Japan as Akumajō Dracula X: Chi no Rondo and the game we knew as Castlevania: Symphony of the Night was released in Japan as Akumajō Dracula X: Chi no Rondo.
"Castlevania? What game is that" is the kind answer you'll get in Japan if you use the western name.

Konami uses shorter portmanteau name Castlevania for western market to avoid potential religious sensitivities and create a punchier branding.
They're also used to change the cross and other Christian symbol of the games into different kind of symbol.
It would be difficult for Japan market if they have to leave Dracula's legacy since Dracula's the core of the franchise.
That's why in the upcoming game, Castlevania: Belmont's Curse (2026), Count Dracula serves as the main iconic antagonist again.