I don't mind the castle having similiar areas here and there, castles feel more like castles having consistent theme to its architecture. yes we would like variety too, but it has to have guidelines so it doesn't feel like a fun house. Also I like castles being totally indoors, instead of partially indoors, then outdoors, then indoors, etc. I really hated how Cainhurst castle in Bloodborne was mostly outside and on the rooftops. Dark Souls 2 Drangleic Castle is entirely better in every way (well yes even Drangleic Castle had its outdoor parts, but castles like SOTN were great because they were 99% inside the castle, well ok, about 40% of it was underground, but um hey, was Circle of Moon 100% indoors castle? I dunno, well it has underground too. um, Order of Ecclesia castle I think was 100% indoors, but the problem was that OoE was mostly about other locations in the land, not just the castle, so its castle had very few bosses and few rooms compared to other Castlevanias.
but yes, the bigger the castle, the better the exploration. and even with similiar rooms, it really comes down to the level design and connecting the rooms that makes the exploration better and stuff. room diversity can be cool, but things will be interesting with items found, enemy types, bosses, and more, so there's going to be new things to see, even if the walls are made of the same stuff.