Developers at the time were going for anything that was "next gen", so anything fresh, cool and exciting was the philosophy. They knew that if it felt old, everyone would accuse their game of being 16bit-ish (as a derogatory term).
I think all 3 games you mention were trying to accomplish this, using different approaches. Shinobi went for digitized graphics and FMV cut scenes, Taromaru went for lots of polygonal backgrounds and SOTN went for an elegant mesh of PSX next gen hardware abilities. Out of those 3, I would say Taromaru is the only one that was perhaps deliberately old school, as it seems the one that is trying the less to impress. Heck, perhaps Shinobi as well, since Sega didn't seem to know what the hell they were doing back then. But I still feel like SOTN was meant to impress and not harken back to the old, other than it being mainly sprite based 2D.
Thankfully, as you stated, Konami was stubborn and perhaps confident enough in the power of the Castlevania franchise, to use it as a way to show the world that next gen didn't necessarily mean going 3D.