[opportune]

>but they don't represent the middle of the distribution

Really? I don't think most middle-of-the-road engineers, given certain requirements, could come up with a working solution in any reasonable amount of time. For example if you just told an engineer "Implement a basic server that can execute queries based on this language spec, where you upload tables as immutable tab-separated text files" I'd guess only the top 5% of engineers could get something working in less than a month.

I don't think that executing tasks like this is something that innately only some small x% of engineers can do. For example, almost all engineers will lack at least some of the skills needed to complete any sufficiently large task: best practices for translating a query to a query plan, how to do efficient Ser-De, what data structures to use to implement the data, etc.

But most engineers lack the meta-skills or traits needed to complete the task. For example, would they first look at how basic SQL implementations and toy projects work? Look up some of the theory of RDBMS? Would they know how to write good tests, good class structures that don't require refactoring in 2 weeks as they understand more portions of the problem. Would they try to roll their own query parser or use a standardized tool like antlr?