> The oldschool forum format requires a lot more scrolling and superfluous content that is unrelated to the discussion

On the other hand, the flatness and default chronology of those scrolls provide a reliable WYSIWYG experience the Reddit trees lack.

E.g., forum noob reads scrolls and sees X% of $bad. Forum noob posts new scroll prepared to get tolerable level of $bad (or hopefully less). Forum noob2 then comes and considers X% of $bad intolerable. Forum noob2 gets deterred from posting a scroll.

Tree noob reads trees where the visible branches do not contain $bad. Tree noob gets unexpected level of $bad in the first Y minutes. After Z minutes, 100% of $bad has been folded away into hidden branches.

After Z minutes, Tree noob2 reads the tree with no visible branches containing $bad. Tree noob2 decides it is safe to post a tree...

Same problem for branches shuffling over time. You can read the Bitcoin pizza guy's scroll today in the same order everyone else did. But even on HN, how do I play back the branches shuffling up and down for the responses to the initial post about Dropbox?

On the other hand, comment trees encourage shallow content highjacking the top comment thread with little to no regard for preceding comments.