PEK at least has some decent traffic to justify it's grandness!
But for absolute over the top grandness relative to the number of aircraft movements, for a medium size airport the prize would have to go to the ghost town that is KUL.
And my favorite -
BHY. I recently had a visit to a place called Beihai in Guangxi province, China. It was a mini-PEK. It had six gates - four with airbridges and two without. Massive departures & arrivals halls. So what you say? According to flight timetables (and departures board) BHY has only 4 or 5 narrow body services a day (not simultaneously either) - an airbridge each. I guess they do have grand plans for the place!