IOW, one may postulate the Sun as a hypothetically stationary object for his thought experiment and the math will work. He may transform coordinates.
But CMB measurements from the 1960's forward confirm that the Sun is not stationary. Nothing in the universe is stationary. Space/time itself is expanding.
But Zero Sum's postulation would not "entail" that the Sun must "agree" to stand still, so to accommodate his/her thought experiment.
So what's the point of the thought experiment?
As it stands, it has no "stationary object," no anchor or criterion according to which its phenomena can be compared and judged. JMHO FWIW