Oh, I'll take Arien out of that statement. Maybe I don't know how to use her as well as the other characters, but she isn't as cheap as the other new characters.
Lime, Krieg and Yuki on the other hand are nice though.
Arien is cheap just because those Phoenix birds have a low cool down and can't be canceled. You can just spam them and run away. they have a wide range and a lot of damage if you max them, shes fun to play with though.
Here: (I made it a spoil button if you didn't saw her yet or her attacks, you never know...)