Death is my most used splinter, but due to some months away from the game my rank is probably too low to compare with you, but I would say if you have some lvl in the cards (depending on your enemy in that rank) you will be able to win more than 50% of the times, especially if the Mana is capped at 17 or 26 (really good combos).

I have the same trouble with Earth splinter, always skip or I try to pass it but always fail...