This has less to do with the power of thieves and more about how various code changes have boosted the relative power of assassins.

I would propose removing the assassin class and in its place create an assassins path within the Rogue class, which encompasses the other "thief" paths with which we are all familiar. An assassin who studies poisons? A trapper who learns vanish? I can think of several cool builds.

Not a popular idea, I am sure.