This is probably true if you're putting a reverse proxy in front of a traditional three-tier monolith, but a programmable proxy is often useful. Sure, you can extend lots of proxies in C or Lua, but most application development groups don't hire for expertise in those languages (and may not have adequate library support in those languages).

If you're a .NET shop, it seems very useful to have a reasonably fast toolkit for deploying specialized proxies. It's still early days, but I'd expect this to become as fast as anything written in Go or on the JVM, which seems sufficient for many use cases.