Isn't there something to be said for splitting up the comments, so you don't get a single thread that covers five different points and nests forever?

No, I don't think there is. They are all still broadly on the same topic. Imagine if I made each sentence here a separate reply. I mean, they are separate sentences and could conceivably be responded to individually, but it would still be pretty silly, wouldn't it?

The only case I can see for doing multiple sibling comments is if you have several truly unrelated thoughts that each deserve a deep treatment. But that's not what's going on here. As cheery noted elsewhere, he/she simply didn't know you could edit comments.