WP Rocket can be a real headache. It generates static copy of your content, but tries leave untouch those parts that should be dynamic, or should be static really short time. If you are lucky enough to find rule that disables caching trustfully on comments it works — but you start loose benefits what you got.
Cachingwise WordPress is… not excaly nightmare, but close. I dumped WP Rocket because it needed too much watching and my time, and works the best with quite short TTLs. I got better results using other tools (and then should be really realistic: is there any solid points to try kill a second if it needs my worktime several hours and almost every week; disabling unnecessary plugings and choosing right theme is better option).
Most of sites actually doesn’t need commenting because those get comments quite rarely and then Discourse as comment section serves other purposes. But of course it depends.
For me connection to Discourse acts as an ad. But most of my visitors are using phones and almost never scroll down enough — totally same questionmark than sidebars are.