Sounds like your battery is degrading due to faster charging and wireless charging. Do you notice if any of these warm up the device?
Mines still have 100% capacity with cocunut showing 2800mAh, also various battery apps, compared to designed 2716mAh since got it on launch date.
I'm not the person you were addressing, but I have only used the included iPhone 5 watt and 12 watt chargers on,my iPhone 8. I am seeing worse degradation than @0014
I charge in the iPhone leather case, but there is no warning from Apple against charging with this case on. In fact, I would venture to say that it would be harder on the phone if I took the case off every time I charged it (wear and tear on the buttons).