I think I've only ever heard "card shark" used to refer to a person who is really into the game, plays it competitively, and generally knows the probabilities of various hands, but generally isn't counting cards or otherwise keeping track of any hidden game state. They're also generally into betting strategy, bluffing, reading people's faces, and other such things. I don't think I've ever heard it used to refer to someone playing to win by counting cards, except in case where card counter is mistaken for the above.