In a single battle, luck is important. But over the course of multiple battles, the luck averages out. Consequently, the winner of a single-elimination tournaments may get there thanks to luck, but the top ranked players on the ladder, not so much. Use or non-use of luck is itself part of the strategy. You can build your team to be more or less susceptible to luck. The classic example is the power vs accuracy argument, eg. Fire Blast or Flamethrower.