Every raid has some kind of theme for its mechanics. In Kings Fall it were auras, in RoN it was dark and light, in Garden it were confluxes and now its about the 3 shapes.
I think it's important to have a theme but also that there's variety in how it's used. The first 3 encounters use the shapes as pick ups for the resonance, Encounter 4 has the shape puzzles and Witness has the 3 different arms.
Imo it would have been really boring if all 5 encounters were centered around those plates and pillars.
I understand that shapes were a consistent theme throughout the raid but the way they were included with the plates and pillars really put them in the background like they are only there for the plates. Made it feel like plates were going to be the main focus of the raid that they would keep adding onto and then they completely changed it. I really like how they focused on shapes in 4th encounter and then added the ghosts onto it and wish that was more how the first few encounters were with shapes being the main focus.