I’ve always charged my phone with 1A chargers in an attempt to preserve the battery. My current phone is an iPhone X I bought at release in Nov 2017, and the battery health is still at 89% according to the battery information page. Subjectively I still feel like I have good battery life too.
I also purchased an iPhone X on release day and never cared how I charged it (iPad charger, iPhone charger, laptop). My battery health is also 89% — though I do not feel like I am getting great battery life anymore
Anecdotally, I have an iPhone 8 Plus that for the last 18 months or so I've nearly exclusively charged with my Macbook Pro charger, and the battery health is at 82%.
