This is a good discussion which, I am confident, we likely have had many times here. Respectfully, I suspect that a floor can improve the sound of a cabinet only when that cabinet is not properly "tuned" all buy itself and needs the floor for sonic reasons. Even then, it would need a certain kind of floor for this. But if the cab is already properly tuned and needs no help from the floor, then the best floor for it to sit on would be one that contributes nothing. A concrete floor, I suppose.
Sure, floors can add boominess. But boominess plays tricks on the entire room. Perhaps you like the way it sounds on stage and the people in the back of the room can't hear the individual notes. I say get the cab off the floor. And yet....in practice I do not follow my own advice.