I really like the changes. You went back to some sort of square one, but it helps to see it in a minimal way so things can be re-added but carefully considered.
My suggestions would be to color the [categories] with css as the same color/style for the drop down in the upper left so there’s visual cues with the associated category colors already established. For the names, maybe we could take a page from the OP meta bar and style it in a similar fashion so avatars still can be seen, since most use the avatar as a quicker visual cue than text. Like this:
That way there’s only two avatars to each topic list item. The OP and the last reply. Instead of what we have now which includes five avatars instead of just two. Not to mention the OP meta bar already has this information (who has participated in the discussion so far).