Most of the 'new' features in Android over the past 5 years have been available in custom ROMs during that entire time. While there are, indeed, minor improvements for the average user, it's been very minor, and leaves you wondering why they didn't have it in the first place (or it's exclusive to Pixel or some shit like that).

And the average person won't even notice most of the new features/improvements; perhaps the biggest one is the camera, and that's all done in hardware or AI these days, which is not Android per-se than a photography app (which, again, is usually a Pixel exclusive)