The player losing the treasure gets to pick the specific one you steal, so you’re unlikely to get something highly valuable unless that’s all they have. (The best time to raid is often right after their first ship returns home. Or, just make multiple raids.)
The rule to reveal treasure immediately is carried over from the illustrated rules, and ties into the “more than half” rule for ending the game. It’s not exactly the best way to handle the endgame, so feel free to continue ignoring those rules and keep using the multiplayer rules for everything instead.