I've always preferred bulky Thundurus to Zapdos. I used a similar set in one of the Wi-Fi friendlies (T Wave/Tbolt/Swagger/Rest) but I found it difficult to use effectively in the end. Not fully sure why as I could always see the potential, but only having one attack always seemed to hurt me.
A lot of Japanese players like to use Swagger Thundurus w/ Lum Metagross, and then paralyse your team so compensate for Metagross' low Speed. They also do the same with Safeguard + Swagger Cresselia, then go with Icy Wind or Thunder Wave as well. This means they can use a resist berry item instead, but they lose Prankster and are susceptible to Taunt more easily. I've only really seen it used in conjunction with Metagross / Tyranitar / Hitmontop, but I think it's safe to say you should at least somewhat expect some kind of Swagger combo if you see a Japanese player with Thundurus or Cresselia at Worlds.
Lum Berry could be a key item in some games if you can manage to predict Swagger against one of your special attackers, and switch in a physical Pokémon with Lum Berry. However, the Japanese players are very clever, they might start to favour something entirely different for Worlds. But this has been a common occurrence on W-Fi all year in my experience.
Also, in regards to the seniors battle and time stalling. I am assuming that was a critical hit Volt Switch against Metagross early on in the match. Metagross seemed like his way out of a lot of things in that game and to have it effectively removed from the game so soon put him on the back foot. I think this is one of the reasons for such time stalling, I would have done the same.