Okay...we're working from equal definitions now

Yup, this would be a universal claim. And we can prove that, at least in our region of the universe, based on the properties that we've observed, that light doesn't need a medium to travel through. However, while we can safely
assume that this is the case throughout the universe, we cannot
prove it...unless we are able to observe the properties of light throughout the entire universe at this present moment in time.
Some examples: the light that we observe from distant galaxies is thousands, millions, and even billions of years old. We can make basic observations about that light, and the places it came from...but that information is in fact outdated by up to billions of years. Can you prove to me that the laws of physics have not changed in those regions since then, and that light now requires a medium to travel through? Or can you prove to me that there are not regions of space that we have not observed where the fundamental laws of physics differ, and light requires luminiferous ether?
Your arguments are now drawing closer to my own...despite the fact that you are entirely unable to prove that luminiferous ether does not exist somewhere in the universe, you feel safe -- based on your understanding of how the universe works in our own local region -- in reaching the
conclusion that luminiferous ether does not, in fact, exist anywhere in the universe, and that no matter what part of the universe we are talking about, light does not require a medium through which to travel.