We encountered the excess post load problem, but the other way around. Having WordPress poll ~15k posts for updated comment counts via the plugin caused crazy scaling issues on the remote host.
That said, we found value in having the stubs in Discourse, and they didn’t create substantial noise as the category article comments fell into was suppressed from the front page using the ‘Suppress this category from the homepage’ option. The titles were usually descriptive enough that search would find the stubs, and direct the users back to pages on the content site.
It may be that for knowledge sites this setting is preferable, but for content entities the stubs almost certainly have value, particularly when the plugin embeds the excerpt and link back to WP. @simon has some approaches in mind to tackle the issue of load, at least on the WordPress side.