The way you describe it; I would agree. You can "do anything" on Android, but this leads to poor implementations for common things.
What I'm referencing is that the OS and Apples own applications are built to support what I would be consider very sane defaults (as in, it supports me doing my own thing, without the need for plugins/modules).
My experience is that on Android I had to have many third-party integrators to get things up and working, and they were very poor quality and would run in the background murdering my battery life. (and I had to pay for it: https://play.google.com/store/apps/details?id=at.bitfire.dav...)
IMAP/SMTP Were less of a problem but it always /felt/ very third party when using tools for that purpose, where google mail was truly first class. On iOS I don't feel this way at all, once I had push notifications set up the experience was identical (if not a little better with my own server due to apples SMTP servers getting overloaded).
So, you're right when you say that Android is more modular and supports stronger composibility of the system. But the experience of actually using it is so incredibly poor that even with Apple doing it's bullshit (no small phones, no headphone jack, protruding camera) I have very little inclination to go back- the "feeling" I get is that it's funnelling me to third parties, whether it be google or samsungs awful "samsung cloud ecosystem"