Here's a replay of the final Grandmaster Cup (Chinese version)
As you can see the winning player used Taskmistress and Druidess. Now What I was amazed about was Taskmistress's level 10 skill (And how, even a P2W whale can get her to level 10).
It cloned five creatures and sent the same amount of creatures back into the enemy deck. The player was instantly granted immense Board Control and won the fight.
And druidess starts warding 3 creatures at level 5 or so... She was damm strong too.
What I am trying to say is that the non-farmable 5* s are extremely powerfull when leveled up (Even Hydra, for that matter)