I agree that the show has been pre-recorded in all recent years but I'm not sure parts or all of it wasn't live last night. To your point, it had too many imperfections to have been a contemplated take.
At minimum, all of the vocals were live. You could see the dynamics changing in Usher's voice as he moved his head, hear his breathing as he danced, etc. I'm less sure about the backing tracks.
My crew commented that the show wasn't as good as they expected. I agree it wasn't, but I told them that some of it was because Usher was courageous enough to do some of it live, and what they were hearing was a normal live show without the benefit of pre- or post-production.