That's a bizarre statement. I could be incredibly familiar with nginx, apache, varnish, etc., and have a website that scales to a huge amount of users and still have no idea how well Caddy scales compared to nginx due to having no prior knowledge of Caddy's performance. Indeed, questions about scaling and performance are going to be some of the very first questions asked by anyone running such a site - that's going to be one of the single most important characteristics about it. (Hopefully after security....)

I'm glad tour aware of the performance characteristics of gp's site!

But seriously, how do you know what their site is? Perhaps they're serving a lot of static content out of memory and a fat pipe, in which case the web server would in fact be a bottleneck.

Apache was an unstable bottleneck before I set up nginx as a reverse proxy.