I have no evidence at all, but I think open source projects create more jobs than it "destroyed" because it reduces the cost of doing businesses of tech startups at critical growth phases and makes them viable by allowing fewer employees to do more. Without open source, companies would employ more people per company, but have much fewer companies overall, IMO. Additionally, salaries would be much lower because skills wouldn't be easily transferable between jobs - hence lower competition for employees.

I've wondered this for a long time. Or if it had a depressing effect on wages. FOSS certainly helps with productivity. Though I believe it's very likely also depressing wages and reducing the volume of software jobs.