I only play casual to test a new deck. Once I get down the deck synergy, I go back to ranked. When the expansion first came out, I chose SK for the challenge, mastered my own warrior deck (no online help, I build my own decks) then went to ranked and saw how powerful it was. I'm bout to try a new monster deck for the next challenge.
Pretty much I use it for testing a new deck or if the deck I made that I like has no chance in hell of winning in Rank.
I agree, using "ranked" style decks in casual is weak. If I see SK in casual, unless I'm testing a counter deck for SK or somehow using a competitive deck, I forfeit.