What do you mean? With the current internals, a 300 posts HN page would weigh ~500kb; different ones will hardly be more compact. Where is the «struggle»?
In March this year, HN changed pagination behavior. Previously, one needed to paginate through pages to read more than X comments. Around March, they now serve all comments at once.
A post having over a thousand comments is extremely rare so not a big deal.
HN has been known to fail in the past with heavy or high velocity threads to the point that dang has asked people to log off en masse to reduce server load. That shouldn't happen for a simple text forum.
