"Perfect information" is a term of art for games, it doesn't literally mean you are omnipotent.
In this context, a strategy is a function that maps every history of moves by you and your opponent to an action. So, while chess is theoretically a game of perfect information, in practice it is less so.
Real war is not a game of perfect information, because you do not know all the strategies available to your opponent. In addition, you and your opponent's priors may have an intersection of zero measure which makes things very interesting.
War is what happens when a certain kind of people try to play the game of chicken which is usually not taught in the kind of fun programs like master's of international studies for members of the preferred party because it is too sophisticated due to the fact that it admits an infinite number of Nash equilibria ... instead, such programs prefer to focus on prisoners' dilemma which, having a dominant strategy equilibrium, is more suitable to ensure such students can go back to the bureaucracy after having passed their classes with perfect As and get us in to war.
Edit: it would be similar to your example of war if you e.g. couldn’t see their pieces or something that would cause information asymmetry. This would make the game very different so clearly the term of art _is_ useful and important.
Yes it _does_ communicate something interesting. It is a basic fact about the rules of play. If there were imperfect information, it would be a different game. Poker with perfect information means everyone plays with their cards up. It is a fundamentally different game.
The fact that chess has perfect information for all parties is fundamental to the game.