They are ridiculously easy. I use a fully upgraded 40-card Gravity/Earth control with 95%+ win rate and 60%+ EM rate at a guess. The Half Bloods having random composition decks just don't have the capability to dish out anything too specific, making them incredibly weak to control decks. I only usually lose when it's something like a one-Pendulum starting hand and with no Towers or Pendulums in the next few draws, early immaterial spam, etc.