Had my 6P for a week now, and my experience with charging is like this:
Plugged into computer with supplied A-C cable: "Charging Slowly"
Plugged into wall outlet using 1.0A charger and A-C cable: "Charging"
Plugged into wall outlet with supplied 3A charger and cable" "Charging Rapidly"
I also tried some experiments with other chargers/cables.
Using "Cable Matters® USB 2.0 Type C (USB-C) to Type A (USB-A) Cable in Black 3.3 Feet" with an older 1.3A wall charger, I still got "Charging Rapidly"
Using "iXCC® Dual USB 4.8 Amp (24 Watt) SMART Universal High Capacity [High Power] [Small Size] FAST Car charger" with the same "Cable Matters" A-C cable got me "Charging Rapidly" This is a dual port car charger, each port is 2.4A.
Using "USB Charger, GMYLE 11W USB Dual Ports Type C & A Power Adapter AC Wall Charger " with "USB Type C Cable, TechMatte USB 2.0 Type C to Type C " cable, I got "Charging" only.
The GMYLE charger supports both Type A and Type C ports, but has an intelligent chip to determine what voltage to supply, up to 2.1A per port. Curiously, it did NOT give me "Charging Rapidly," perhaps because the phone was at 85%. When I tried the phone in my car, the 2.4A charger DID show "Charging Rapidly" with the phone at 81%, so that is strange.
The "Cable Matters" cables are on the thin side, but they do not become warm when "Charging Rapidly" so I'm not worried about any fire hazards.