Let's enjoy the final days! Check out what changes and events started this March here: http://maplestory2.nexon.net/en/news/article/56485/sunset-in-maple-world
MapleStory 2's servers will be officially closing on May 27th: http://maplestory2.nexon.net/en/news/article/56486/service-discontinuation
Not sure where you got that information but I can assure you that Thief is anything but low tier. Unlike most classes Thief requires strict input with it's combos and good cooldown management for you to be effective in both high level raids as well as pvp. That said, Thief, if handled properly are consistently top 3 in DPS in lvl 50 10-man raids and is constantly fight for top pvp ranks along side Strikers (which we won't have on launch, rip) in KMS2.