Stealing signs while standing on 2nd base has always been "legal" that's not cheating it's baseball. That is part of the game. Using technology to do so is downright cheating and no it shouldn't be allowed. It's a monster advantage. Maybe as easy as looking at Mookie 2018 vs 2019 to understand. Mookies a very good player but even better knowing what's coming at him, if he's sitting on number 1 it's almost unfair to the pitcher. He hit .361 at home in '18 and .316 in '19. His average overall about the same difference. If they were still cheating this year they didn't figure it out well I guess but probably laid off after winning it all and stepping over the line on this.
I don't think it's likely that it plays a major role. It really only applies (
as the Red Sox supposedly did it) when there is a man on 2nd or maybe 1st base, and they are deep enough into the game to have given the signs to the players. Then the guy on base has to tip off the batter each time. Is there some evidence (we can certainly watch replays) that this happened? The Astros tipped the pitches live via banging on garbage can. Quite a bit worse.
So get rid of the video replay room access during games or have it monitored as it was in the playoffs. It is certainly ok to watch film of past games to steal signs and I'm sure every team does that. Even in the middle of a series. So unless teams change signs every game, they are vulnerable.
I guess my point is that it doesn't impact every at bat, and like roids, every team was doing it. Baseball needs to make sure the playing field is level, but other than that it doesn't really matter.