What was it? Personally, the only thing I miss from stock Android is the Google Wallet/Pay/Wallet. (I do use microG to get push notifications and embedded maps working.)
Once my ability to run a "background spyware-less" Android device went away, so did my willingness to put up with the negative sides of the usability tradeoff.
Apple probably sends some telemetry home, but at least their business model doesn't depend on knowing the exact Pantone color of the food I ate for dinner to market a matching wall paint to me.
Edit to add: oh, yeah, you mentioning 3P apps complaining if they detected root or MicroG reminds me of many a horrible night of debugging. Ugh. What a mess.