To me the current preparations are mostly awkward traps with longer setup intervals and ultimately a gimmick. What they could have been though is a series of skills centered around counter zerg abilities. It even makes sense in the context of the class in the game.
Imagine stealthing up, dropping a preparation in the path of a zerg, then popping a massive boon strip preparation. Stealthing into the backlines to drop a knockdown prep that ignores stab or is a big damager with a large player cap. A few thieves could disrupt large zergs for some very interesting counter play.