I think you may be both correct and perhaps there is a bit of confusion because of not well defined term us. I am a little confused by both arguments as we seem to have several concepts jumbled up together so try parting them .
The first concept is physics homogeneity. That basically says
1.) No point is space is special the laws of physics are the same everywhere
2.) No point in time is special, so the same basic laws of physics should govern all of time.
3.) No direction in space or time is special moving in any direction the physics laws remain the same.
So what do you both think of the concept of physics homogenity?
The second concept is universe expansion and it being uniform and homogenious. So if the universe is expanding like a ballon not uniform would be the idea on part of the ballon has a weak spot and that section may expand faster than another so you get a ballon with bubble spots
I think you need to work out we are not mixing those two ideas in before discussing motion?
If you are both happy to have homogeneity in both of those two concepts you can move on to discussing motion. If we don't have that agreement it gets more complex to discuss motion.
