Earlier quoted context omitted.
It is a great choice for a general purpose proxy. (That's kind of the point.)
But they mentioned that they wanted to use C++ instead of go to get even that extra performance out. I use Caddy a lot and it's perfectly fine for my scale, but at dropbox's scale, maybe go wouldn't be enough for the ingress part?
I am more curious what makes the author think Caddy "might not be the best choice for a general purpose ingress/egress proxy" (there were no other qualifications to that statement, but no evidence to support it either).