The on-chip GPU Apple ships in their MBPs draws way less power than the dedicated Nvidia chip. This is especially noticeable in the battery life drop that occurs when the dedicated chip is used exclusively.
On chip/package has many power advantages, and Apple is on a much newer process node with M1 (TSMC 5nm).
The point I was making was that e.g. a GTX 2070 desktop has around the same compute power as the mobile version, but the mobile version uses much less power. It does this by being beefier (2560 CUDA cores mobile 2070, 2304 CUDA cores desktop 2070), but running at a lower clock.
