CGI can be used for high performance sites/routes when used with HTTP caching. Though CGI leaves response time on the table by taking arguments via the environm

CGI can be used for high performance sites/routes when used with HTTP caching. Though CGI leaves response time on the table by taking arguments via the environment such that you can't start/pool CGI processes before requests are arriving. FastCGI needs multiplexed transport of HTTP traffic in to and out of a single process, changing code complexity drastically and taxing memory management. It's far from keeping CGI's simplicity.