If we are supply constrained on batteries, you can't just ignore this. It's e.g. either 1 full electric and 5 gas cars, or 6 plug in hybrids.
You don't have to ignore the lubrication oil etc. as you are saying. Just look at total carbon for the two alternatives (not the only options, less cars and more buses is another option).
Slowing production may be bad for the laborers of the company in the short term as it probably means fewer factory shifts and fewer workers get paid, but it also means less downstream supply of cars on the market, potentially an increased pressure on price to meet demand, so also potentially good for the company bottom line if they demand higher prices during the constrained period.
Slowing production would be great for total carbon output.