Here’s a good example, this topic has 1700 posts.
Summarized it’s reduced to the 100 replies based on the underlying interaction stats which Discourse collects.
It’s incredibly effective at cutting through the cruft.
The tools already exist to make consuming or managing large topics quite straightforward. Not even trying the feature undermines any criticisms or calls for alternatives.
OTOH, if you try it and dislike it then there’s an opportunity to provide feedback on posts which were picked up or missed. You can help make the feature more useful and relevant to everyone.
Maybe. Regardless, no topic needs to be 20,000 responses either. Creating serialised topics or just daily topics achieves the same thing, and Discourse being Discourse a bidirectional link between them is maintained when the new topic links back to the old.
Heck, if you’re really determined you can automate that process, but it really shouldn’t be necessary.