What you’re seeing is essentially the inadequacies of your Apple screen. Whatever i1Profiler and the ICC profile it has created need to do to get your screen to perform to the specifications you selected and also whatever specifications X-Rite has selected for use in their software (but not necessarily told us what those selections are - maybe better colour accuracy, at the expense of smooth gradients).
As I just mentioned, it is quite possible that i1Profiler is more heavily leaning towards having accurate display of colours rather than the absolute smoothest gradients and most perfect greyscale possible. In fact, that is another major drawback of a screen like yours, in that it doesn’t have such great neutrality and greyscale performance. And when I say a screen like yours, I am referring to all non-hardware calibration type screens and those which may or may not be genuine, physical, actual 8bit screens - without needing to resort to dithers of one kind or another.
One must also remember that if profiling and/or calibration is being performed on a non-hardware calibration screen, a screen which does not have high bit-depth internal LUTs, say 12-14+ bit LUTs, any corrections the profile performs will by necessity take away displayable RGB levels and that’s also a possible reason as to why your gradients aren’t looking so great anymore. Your screen/profile combo, after profiling, doesn’t have 256 levels for each channel of R, G and B, but may only have, for example, 180 blue levels, 200 green and 220 red levels displayable. These are all just for example, I’ve no idea what the actual number of levels your screen now has available to display but this is the general idea for you to understand why you’re seeing the things you’re seeing.
Maybe what you need to do is trial a few different profiling applications or even play around with the options in i1Profiler and see if there’s anything you can do to improve your situation.
Does that help give you an idea of why you’re seeing the things which you mentioned?