At 50% overturn rate, this is literally a coin flip.
Here is my new proposal: With gambling playing a larger and larger role around the game, we should introduce it directly into the game. No limits on the number of challenges, but every one is a double-or-nothing situation.
Umpire calls a strike, hitter challenges . . . challenge system upholds the call, now it is TWO strikes.
Umpire calls a ball, pitcher/catcher challenges . . . challenge system upholds the call, now it is TWO balls.