Okay, let's make one of the easiest of comparisons: Vivillon vs Adamant Charizard-X

Turn 1
100% of the time:
Vivillon uses Sleep Powder, Charizard can't do anything

Turn 2
66% of the time:
Vivillon uses Substitute, Charizard can't do anything
33% of the time:
Vivillon uses Substitute, Charizard uses Flame Charge and wins

Turn 3
50% of the time (if you make it to this point):
Vivillon uses Quiver Dance, Charizard can't do anything
50% of the time (if you make it to this point):
Vivillon uses Quiver Dance, Charizard uses Flame Charge and repeats the cycle

These paths aren't yours to choose, beyond the moves you select. They are undeniably based on which outcome RNG picks, as opposed to a scenario like HP Electric vs Grass Knot in Greninja vs Gyarados, since in that situation, the choice is entirely on the players, while above, it is not.