I see. so basically...
Ghostring users can be killed by:
-asura with civil or turtle general cards if hp is low
-changing their element
Deviling users can be killed by:
-spamming finger offensive with converters.
-High Wizards xD
And that's it huh...
Hydra does almost the same thing as civil servant/tg, since humans don't change their race. They're still demi-humans. Civil servant will only work when the enemy is wearing ghostring so it's not as viable as hydra/skel worker/turtle general.
Also, if I remember correctly, different card effects stack multiplicatively. So when you add 2 Hydras and 2 TG cards, it doesn't mean that you have 80% bonus dmg on demi-human. It means that your dmg for example is 100. 100x1.4x1.4 = 196, where quadruple bloody would only get you 180.
In the private server I used to play in, champions had to have at least a GR armor and an unfro armor for switching since most people have DMG weapons, and frost weapons.
In addition, it's possible to 1 hit someone as long as you the person wearing gr/devi has low max hp as has already been stated, or if you simply have too much damage. Increasing damage isn't necessarily limited to your weapon and its cards. High upgraded headgears with slots can have a carat card compounded to them, or if high ups aren't present, incubus cards will suffice. D. Rings and Nidhoggr's Proxy Skin Fragment also have moderately high SP bonus.
Lastly, as for 1 hitter champions with Lady Tanee, yes, they can simply one shot you with an Asura Strike.
I guess it all just comes down to how well equipped you are and how much resistance you have.