It costs so much not because of the first strike ability and its 2/3 power and toughness, but because of its activated tapped ability
What makes Thalia so good is that it taxes all players in the game, forcing them to pay an extra one generic mana to cast their noncreature spells
Yorvo is an efficient threat that allows the mono-green version to freeroll Nykthos, Shrine to Nyx
Rogues are often related mechanically to mill, so you can have an aggressive/tempo build with rogues attacking every turn and have mill as a subproduct
For the rare few that manage to get ahold of such cards, they may have a life-changing amount of money on their hands
From there, he managed to stop Nicol Bolas, who was plotting to throw Alara into chaos by recombining all five shards and unleashing the hell of Grixis upon them all