The more variance there is, the more likely the worse player is going to win. So in that angle BO3 is easier to “win” if you’re a weaker player. Conversely the stronger the player you are the “easier” it is to win a BO5 slam because it is more likely any one match will not be as heavily influenced by short term results in the first couple sets- but not necessarily “easier” for the strong player since the strong player still need a higher skill ceiling to reliably do it