Here's the sample screenshot from the original announcement (nearly seven years ago) of the (then) new activity page. This is what I remember it looking like as recently as yesterday:
Here's what it looks like this morning. The top part is similar, the bottom part is formatted very differently, with a much less dense presentation:
I couldn't find any announcement that the page format would change. Is this something wrong in my local configuration? I very much preferred the old dense version.