It doesn't really have much to do with the mining. The embodied carbon of the battery comes mostly from the fact that it has to be baked to dehydrate the materials. Carbon, because there is not enough renewable energy in the places where these batteries are made. As time goes on the carbon embodiment will decrease.

The overwhelming problem with giant electric SUVs is the opportunity cost. Given limited capacity for battery making, and considering that we are using the last bit of our emissions budget to make them, it is obviously better to make them as small as possible. Slapping a 180kWh battery pack in a Rivian is ridiculous. With the same materials you could make 500 electric bicycles.

How’s that worse than continuous fossil fuel extraction, refining, and combustion over the lifetime of the vehicle?

you mine for battery materials once. with an ICE engine you mine for oil over and over and over again, and you burn more fossil fuels to refine it, and burn more to transport it to you, over and over and over again.