There is way more than 5% of the cost from labor, you are missing all the extra costs from the parts they buy from other companies. There are way more laborers working on the cars than what the car companies employ themselves, the small number of workers still working at the car companies now try to leverage that but it is unfair to give all the value of the cars to them rather than share it evenly across the industry. And when shared evenly there wont be much left.

This seems to dispute your claims [1]. Also - you can't count suppliers' employees since they're not part of the union action / demand.

[1] https://www.cnbc.com/2020/01/17/labor-costs-for-detroit-auto....

"Labor costs, at roughly 5%, remain a small percentage of annual costs for the Detroit automakers, according to Dziczek."