It'd be interesting to compare the performance of the author's approach to an analogous design that changes CGI for WASI, and scripts/binaries to Wasm.
No, Linux typically takes about 1ms to fork/exit/wait and another fraction of a millisecond to exec, and was only getting about 140 requests per second per core in this configuration, while creating a new WASM context is closer to 0.1ms. I suspect the bottleneck is either the web server or the database, not the CGI processes.