if there was a significant improvement in the newer SpyderX model(s)
Yes. It is much faster (around 5x) and more accurate, but lacks support for “spectral” colorimeter corrections (whether that matters to a great degree is debatable).
Or if there is a calibrator that is considered to be even better.
Also yes. ColorMunki Display or i1Display Pro, essentially the same instrument, but the Pro is a bit faster. Both are notably faster than the Spyder5, too (4x-5x), and more accurate (especially for dark colors).