That's just, like, your opinion man. I prefer HN's indented approach to a typical forum listing where it's just a firehose with quotes. But the best approach is to allow the view to be switched as desired.
So you get a vast amount of low quality replies above the next high-quality reply.
For low volume it works okay because you can manually collapse but for high volume once it starts paging it breaks down and you just get further into the top level comment without properly being able to escape.
Reddit's model of auto-collapsing so you get a mix of threads and top-level replies is much better for picking out the better responses.
Also for long list of replies, you also only show first few.
This design may helps "smaller comments" to surface when the conversation is relatively "mature".
However, the main issue is that when you can quote multiple comments (when you are in a firehose view) you tend to send a single post for multiple replies; I have no idea how that could be shown in the tree view.
Essentially a firehose is a superset of a tree structure, if your unit is a post.
The potential for problems would arise when everyone Replied using a root-level post to the firehose. This could be mitigated with prominent Reply links on every post in the firehose, with the root-level contribution form deemphasized. So you can quote multiple people but you still chose a parent by choosing which Reply link to click.
One problem is that when people are manually quoting a post, they can edit that quote down to only include the relevant portion of the post they're replying to, and depending on the forum culture unnecessary full-quoting is actively being discouraged.
Automatically added quotes on the other hand don't have such a luxury, so you'd get a big bunch of full quotes, which wouldn't really be ideal, either.