Pure physics my friend. The further away an object is from a fulcrum, the more physical distance it will travel around that fulcrum for every degree of movement at the fulcrum (think teeter-totter). The higher decks have a more even and rhythmic motion than the lower decks (inverse square law: the amount of energy detected is inversely proportional to the square of the distance between the point of origin and the point of measurement) - which is why the water in the QC pool routinely flows out of the pool on either side but nobody really notices - it happens slowly.
Higher rooms are more expensive than lower rooms because movement is muted by the distance from the fulcrum point (keel)
Well the misconception occurs when the ship is considered to be like an upturned triangle, IE people see the front (Bow) and see a point near the bottom and assume that runs the way through, and assume it moves like an upturned pendulum, but in fact, if you look from the back (Stern/aft) you see its square, and the vast majority of the hull, is square.
Therefore everything is relative, and if top/port moves then relative to that starboard/bottom moves. Also bottom/port and starboard/top.
At any point where something is knocked or in contact with something else will move or vibrate more than an other point, ie if you knock a spoon at one end it vibrates more than elsewhere, so at the point where the ship meets the sea (water) has greatest vibration and movement and the ship overall flex's in the water to absorb that, (if it didn't it would snap), and therefore the point of impact of waves is where the force is and higher decks have less force.
Now the point I made and you remade is yes you see some movement at the Cove, Goofy, and Mickey pools on some rough days, this is gentle back and forth, and so a good yardstick to gauge the movement of the ship.
Top deck being welded to the other decks will move relative to each one.
Now the issue for debate is every person notices different things, sea conditions differ, the ship takes on more ballast in heavy seas altering the centre of gravity, and if you are on open decks the wind force will give you a sense of movement, where inside decks without wind will make you feel less movement.
Ships are fully stabilized and try to avoid bad weather and rough conditions sailing around thoose, so most people never experience movement so will all say they are the same. The myth of the top deck moving far more than any other deck is actually impossible but is a common myth.
We most likely will bore everyone on this thread so we should leave it there.
I actually agreed with the vast majority of what your orginal post said.