The alternate design isn't "performing too well" by not telling you which of your friends are online to chat with, like the current version does. It's just decluttering, and relegating that important function to one of many miniscule, unlabelled icons. It's not "performing too well" by rendering links in the same colour as body text, and making the search function look like a header: it's just making them subtly less obvious, which matters when your users are in the hundreds of millions and some of them really aren't that savvy.
(Possibly it matters even more with casual users who are web-savvy, in that you're missing an opportunity to encourage them to search by prominently positioning the sort of medium white box that makes them think about searching)
Whatever is cleanest and most elegant is not necessarily the most user-friendly design, never mind the optimal design from the point of view of user engagement.
Very good observations. You made obvious to me most of what I did not like in that new design. My first reaction to the look of the new design is that is made each entry much larger filling the screen making the text less noticeable and having fewer posts on a page. A useful design for me will be concise so I can scan more quickly.
Whatever is cleanest and most elegant is not necessarily the most user-friendly design, never mind the optimal design from the point of view of user engagement.