Each of the fourteen slots in each booster draws from a pool of 121 potential cards, making each individual card exactly as rare as a mythic in a normal set
And if the Vampire Counts or Tomb Kings player is in a poor position when the general falls, they usually just surrender
It doesn't stop tap down, bounce, counter, exile, sacrifice, -X/-X and so on
They tend to be less frightening than dedicated auto-win cards like Door to Nothingness, and can be useful at any stage of the game
It's worth pointing out that Thrumming Stone also gives the free spells you cast Ripple as well, meaning in a dedicated Hare Apparent deck, it's not unrealistic to expect hundreds of tokens
Archetype of Imagination is a 6 CMC Human and it makes it very difficult for your opponents to block Krothuss/the attacking creature/attacking token copy of that creature