In theory that works but then you reduce the game to a maths lesson.
The game is complicated, it takes time and an encounter can last 2 hours sometimes!! - the complexity is probably the reason a lot of us don't play the skirmish games, if after all it would be exactly what you suggest, monsters on a card and the fun would really go out the window a little.
Good idea in theory but in practice it would over simplifiy a game that relies on complexity to remain interesting