We are big users of WP Rocket (licensed through 2020). WP Rocket works great on our clients' normal busy sites (up to 5 million visitors/month). We run one very high traffic network with up to 40 million visitors in one week or even a million visitors/hour.
On this site, WP Rocket fails miserably. When new articles are posted WP Rocket purges the cache of too many different pages:
- all the category archives to which the page belongs
- related date archives
- even the previous post and previous post in the same category (this is to keep the prev/next links on the posts working, if the post is updated it clears the next post too)
- and of course the homepage
And all of the above happens if a post is added, updated or a comment is posted. So when you have people writing new comments every second you end up with a lot of cache purges on the pages where the information about new comment is not so important - new comments should only purge that post cache and nothing else.