Well, Bentley is making ~9000 cars per year with ~3000 employees. Tesla is making ~100k cars per year with ~37k employees (not counting all the subcontractors). That's exactly the same ratio, and it's bloody awful compared to large-scale car manufacturers. E.g. Toyota has 10x the number of employees as Tesla but makes 100x as many cars. Even if next year Tesla production is 5000 cars per week all year, they will still have >4x as many employees per car built compared to Toyota.

Also, Bentley is fully owned by Volkswagen. If they wanted to "scale up" to a downmarket Model 3 equivalent, they'd take the VW MQB platform, use most of the non-platform components from the Mk7 VW Jetta (probably offering the 250hp and 300hp engines with AWD), spend 2-3 years developing sufficiently distinct styling parts, and then be able to churn out 100k cars per year.