Well makes u think they only have 5 with how long it take for new content to come out. When they had events there would be new ones ever 3-5 months. Perm content like 1 year plus? Not event good content fishing is boring, and the only permanent content they have release. Correct me if I'm wrong tho
I'd guess theres probably only around 5 in each part of the company, only a few support members, a few designers, a few programmers, etc.
The reason they could do the events so often was because they were all basically identical, all they really had to do was change designs (bosses, fashion, lux, etc) and also change stats on lux and loot. I'd guess they didn't really have to do many major changes to how the game operates.
Permanent content is different. It's adding new things to the game instead of just changing things that are basically already set. Also, in addition to fishing we also have cross platform play, the Auction House, battle mounts, pets, and several other things (including cooking coming up in a few months).