That “10W for the screen” includes them all. No.

Taken straight from the LCD deck in front of me: With the screen as dim as possible sitting in the home menu, the total power usage of the deck is 4.9 Watts. The GPU is drawing 0.3 Watts. The CPU is drawing 0.3 Watts. With the screen brightness turned to full but the deck idle, the power draw goes to 7.1 Watts, but the screen stops updating the image after 10 seconds. CPU & GPU are both still at 0.3 watts. Jiggling the stick every few seconds to keep the screen on, the power draw goes to 9.6 Watts. CPU & GPU are still 0.3W each.

Result: The “rest” of the Steam Deck, minus SSD and cooling fan activity at full screen brightness, uses 9 Watts, at least 4.7 Watts of it being the screen and backlight alone, though I was not able to test how much the draw would be of the screen could be turned completely off, as that isn’t possible in SteamOS.

15W + 9W is 24W, we are a watt shy of 25W.