This can’t be an issue - if you use 60W brick, your battery would be slowly discharge and performance would be 20-25W, but temps would be 50-55C (just tested on my FW16). If temps are 100C and power less than 45-50W => it’s thermal throttling. I got very similar on my first motherboard and now after replacement I have ~95-96C with continuous 56W (Example here, on different thread).
Just do few days stress-idle loops by 5-10 mins. In my case temp settled from 100C to ~95C and continuous power razed from 48W to 56W. So looks like Liquid Metal also needs some time to settle. I bought new heatsink and I have PTM7950 (60x60) which I ordered from LTT store - $14.99, applied on few FW13 (few times each) and have more than half left. However, looks like I have good temps with LM - decided to left it as is for now.