Re-read the argument that's being made. I already pointed out several times that the complexity of collision detection would remain the same (in each case, you'd have to consider the distance between your object and the Earth, paying attention to their shapes, rotation, etc.) - it's the complexity of motion where enormous savings can be made - both in terms of time and space.
If you move a complex object, every point of this object is in a different position after the movement, so every point needs to be updated.
This can be either done by ...
... either calculate each point separately (unusual but maybe more efficient for FE simulation because for each time slice it is the same value added to the z axis for each point).
... or calculate the center and orientation of the object and derive other points from it.
The only difference is where the movement for each point is handled - either by the moving function or by the collision detection function.
It's just a shift of the effort from one place to the other but it does not reduce it.
No, you just hyperfocused on replying without processing what you're replying to. You're also the victim of an oversimplified example, but I don't want to hammer JSS for making it simple too much. Once you consider things like parallelisation, the efficiency rift becomes even larger.
That's a (quite common) misconception of parallelism. Parallelism can make things faster, if it is well implemented. But parallelism makes an algorithm never more efficient (which would be less computing power for same result), it adds more overhead complexity.
This might change with quantum computers - but this will also change the algorithm in a way which makes this discussion obsolete.
Neither of those are necessary - all you need to do is periodically reset your co-ordinate system.
Which is the less smart version of "permanently adjust it to the center".
However, given everything we know about time complexity, space complexity, and our state-of-the-art algorithms, RET's case for being more efficient is non-existent.
I would not even dare to guess which one is more complex.