In over 20 years of working in IT I never found a single webdev-type of person that can write an efficient SQL query by himself. Yes, most are able to write a query to bring the correct result, but I saw way too many cases where the perf test on a database with the expected production volume was running in completely inacceptable times and the developer had no idea how to fix that; for each version of SQL perf-tuning is very specific.
Also proficient != expert. I met enough developers that were brilliant in their work to be convinced that 5x developers are not a myth, but they are real, while rare, occurrences. For me a senior developer in X knows the ins and outs of that X to the level that his code is an order of magnitude better in term of efficiency, performance, productivity and security. A regular developer can be just proficient, but it is not what I wrote about.
Also proficient != expert. I met enough developers that were brilliant in their work to be convinced that 5x developers are not a myth, but they are real, while rare, occurrences. For me a senior developer in X knows the ins and outs of that X to the level that his code is an order of magnitude better in term of efficiency, performance, productivity and security. A regular developer can be just proficient, but it is not what I wrote about.