I'm no expert but I definitely can't help but wonder if it's WiFi or Bluetooth. Maybe something like radio interference making it work 50x harder?
Around a decade ago I had a MacBook that was super sensitive to interference issues. Although I'm not sure if that results in a big power draw (the way it does with cell phones for example when you're constantly going in and out of service).
I can fairly confidently rule out Bluetooth, as turning it off in control Center doesn’t seem to affect the power drain. Wifi is certainly a possibility though.
Around a decade ago I had a MacBook that was super sensitive to interference issues. Although I'm not sure if that results in a big power draw (the way it does with cell phones for example when you're constantly going in and out of service).