Heat is one main consideration. You have to look at it in cycles. How many times is the user charging the phone on the wireless charger on a daily basis? So when you have the inconsistency of somebody that charges the phone let’s say ‘9x day on the wireless charger throughout the day, you have that constant cycle of where the battery is exposed to levels of higher heat, then removed, rinse and repeat. That’s what’s unhealthy for the battery, it’s not just the heat, but the cycles of exposing the battery to elevated thermal and then taking it off the charger.
Wireless charging has its advantages, but long-term effects, I would not recommend it. I actually just prefer ‘wired charging‘.