Temporal Fissure might not literally win the game the way Tendrils of Agony or Grapeshot do, but it certainly kills your opponents enthusiasm and desire to keep playing
And you honestly dont need your opponents to trigger it
Trample Whenever this creature deals combat damage to a player, put that many +1/+1 counters on it
I know what cards are powerhouses of a five-color deck
The gems offer more bang for their buck and can be used to purchase a multitude of cards, generally in bigger quantities
It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or any Auras or Equipment attached to it, or any non-copy effects that have changed its types, color, power and toughness, and so on