Core Ravnica is in the blind Eternities of M: tG, which is a very different universe. Plane Shift: Ravnica is a support to run 5th ed games in that universe. Now, nothing prevents a DM from saying "Ravnica is an alternative primary material plane" or "Toril is in blind eternities" and connects the two together. It would be quite easy, whether in cosmology. However, canonically, they are not the same. There are no planeswalkers (canon) in Toril.
Blind Eternities have some similarities with the astral and / or ethereal planes, but blind Eternities are much more hostile to life and function in distinctly different ways.