I don't think this is working properly now.
We have complex jobs that use displayName heavily. We're explicitly using displayName to be able to quickly look at the list of builds and know which one did what. While the main build screen does show the name in the top of the page, the activity screen does not show it anywhere, not even on mouse hover as mentioned in previous comment on this issue. It just shows the build number.
Here are example jobs that use displayName heavily (These should be publicly viewable):
It is pretty important for us to see the right display names, otherwise we can't use BlueOcean to monitor these jobs.