Heretic is a 3D game, as was Doom, since the world is really 3D: in addition to the 2D vectors making up the walldefs, there is a height component in each sector and entity which adds the third dimension. That some parts of the game (entity-to-entity collision, but not hitscan-to-entity which knows about elevation) ignore the 3rd dimension or that the renderer took advantage of the way the world was represented to speed up wall rendering doesn't really change that the world itself is made up of three dimensions.
Entities being 2D sprites is also irrelevant as they are just billboards and many engines even today use billboards for various reasons (particles, foliage, LOD, etc). They are also placed in 3D space.
Wolfenstein 3D on the other hand, yes, that is a fully 2D game as there is no third dimension outside the implied wall height used during rendering.
I mean, it is really simple, there isn't need to justify some old misconceptions about "2.5D" or whatever that persist due to pop culture: if your graphics data has three dimensions, you are doing 3D graphics.
Entities being 2D sprites is also irrelevant as they are just billboards and many engines even today use billboards for various reasons (particles, foliage, LOD, etc). They are also placed in 3D space.
Wolfenstein 3D on the other hand, yes, that is a fully 2D game as there is no third dimension outside the implied wall height used during rendering.
I mean, it is really simple, there isn't need to justify some old misconceptions about "2.5D" or whatever that persist due to pop culture: if your graphics data has three dimensions, you are doing 3D graphics.