Of course what Costa does can be defined as dribbling. That's the whole point actually, you just set up your own definition on what a dribbling is and isn't (for you), limitations that have little to do with reality. Pushing the ball and beating your man with this tactic is not only a valid dribbling, but one of the best and most realiable weapons a dribbler can have, because speed, quick reflexes, power and athleticism are qualities that stay for you for a long time.
And Costa's flair is also there to be seen. Has that bit of joga-bonito in him. In that way, he's superior to Bale, who's dribbling looks more mechanical to me. I much expect Costa to pull a trick out of his hat, than Bale. Although Bale is one of the players with the best technique of hitting the ball right where he wants. Some of his headers and shots are almost perfect.