With Displacement you have to subdivide the mesh to get a decent result, and it’s still a rough representation of the details, and you need a normal map too to get smaller details to be readable, with this you can cut down a map, which usually is 16bit (4 bit per channel).
The procedural stuff you are seeing is probably some kind of pre made models, that are fed into Houdini Engine, and then are arranged depending on how you structured the tool. Have you seen how fast it updates the scene when you do a change, and we are talking about “simple” stuff:
It’s not feasible for real time usage inside a game.