You mean for Caddy http.cache proxy caching ? @Whitestrake advises against it Htttp.cache plugin usage - #2 by Whitestrake but probably because the http.cache plugins needs a few more features like cache or exclude from cache based on key or cookies so you can further fine tune what to cache or not within wordpress.
Haproxy is load balancer not really a HTTP/HTTPS web accelerator like Varnish Cache or Caddy’s http.cache plugin.