> I have done several experiments where, the only difference are a couple of paragraphs describing the technology stack for the AI tools.

The differences emerge as the project goes on. Comparing feature velocity and defect count is difficult unless your experiment is to build the same project over a long timeframe across several languages. Then winners would indeed emerge, but then that's only in the context of whatever domain said project is tackling. For instance, if concurrency or infrastructure isn't a large part of the complexity, BEAM languages might not confer much benefit.