I've been getting regular updates for my Xperias, in the past year they have been very regular, but I never noticed any difference from any of the updates, not once. Not even going from Android 8 to Android 9, everything is always the same, might as well be Android 5.1.1.
Oh, I just remembered, there is one huge change in Android 9 and it's the night light from Android 8. Sony never included it in Android 8, but now we finally have it and it's amazing, just like the similar apps that existed on the Play store since forever. No sign of Android 9 fuctions yet though.