It is a clean design, and that's good, but there's a really long list of things that are wrong with it. Things they could fix while retaining a clean, stripped-down experience. In light of that, I'm confused about why people ascribe so much of the site's success to its design. A better design doesn't have to (and shouldn't) mean a heavier one.

It doesn't seem to have hampered craigslist, though, and that's why my best guess puts it in the "nonfactor" category.

None of what you say Craigslist did wrong obviates the importance of recognizing what Craigslist did right. It seems that what it did right has proven more important than what it did wrong in this case, in fact, further attesting to the value of what it did right.

If you want to do a similar job better than Craigslist did, you should probably do what Craigslist did right, and look for ways to improve it without undercutting those positives. In short, the fact Craigslist does some things wrong doesn't mean you can't learn from its example.