There’s no heightmap node because there’s not just one thing the PBR process does with a height map.
You could use it to power:
- Pixel depth offset
- World position offset on tesselated meshes
- Displacement
- Parallax occlusion, either via the simple BumpMap node or the fancier ParallaxOcclusionMapping node
These choices are nonobvious and have tradeoffs, which are all good reasons for there to not be a simple heightmap node.