That was a somewhat hyperbolic statement. Make an application in node, genie, and rusts actix. Run them and see how fast it takes for the cli to load each of them. Feel free to package compiler the Julia one if you want. It's a good experiment with visual results.
P50 for basic routes using other web frameworks can be sub 0.5 ms. See the techempower benchmarks. These benchmarks are somewhat flawed, but I'd be surprised if genie was faster then flask all around, and flask is widely considered expensively slow.