Casino's didn't design blackjack to be beatable. What happened is that mathematicians discovered it could be beaten, and in turn, casinos have either elected to make it unbeatable by using continuous shuffle machines, or to leave the game as is.
Is it possible to come on top consistently in blackjack? If you know what you are doing and are allowed to play, over the course of many thousands of hands of blackjack you can consistently win money, something like 1.01 times the amount you bet.