Maybe we are speaking of different things. I am looking at the 3.1A (15.3 W) official supply, combined with the claim that the Pi4 can provide a total of 1.2 A to external USB devices, meaning I believe it cannot use more than 1.9 A (under 10 W) all by itself. I am presuming that the power dissipated by external devices would not significantly add to the heat inside the Pi's case, at least if they connect through a USB cable. I agree my assumption might not hold for a small directly-connected USB memory device or other dongle which mostly dumps its heat through the USB connector shell.
Edit: this power benchmark says the Pi4 uses 3.4 watts at idle, and 7.6 watts under load.
https://medium.com/@ghalfacree/benchmar ... e5afbcd54b