In the real world, most software developers are not star performers. The average programmer is fairly mediocre. I have observed this in my 30+ years as a software engineer.

So it's not a "management issue" but an availability of top talent issue. When a company hires hundreds or thousands of developers, they can't all be top shelf. Many will be average talent.

A 4X productivity hit is certainly realistic. A large, complicated language can greatly impede the progress of a project. That's why languages like Python and Go are in such great demand.