I don't think the complaint is stealing signs. That's part of the game. It's placing a camera on the catcher (so no matter how he hides it) and using that to steal. (If the catcher was dropping the signs between his legs, or a shadow revealed them, that's fair game.)
I've seen some really long lengths college teams use to hide pitch calls (college coaches typically call every pitch).
I've also seen (actually after the game the players told the story) a player develop - during a game - a phone app which successfully predicted pitch type called by opposing bench.
Imagine how much of an advantage a batter has on the next pitch after watching an earlier pitch; which hes already decided to evaluate (i.e., not swing) in order to really calculate its trajectory and speed. A credit to pitchers who can win these matchups.