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This is how it'd work, once you select a champion it will display the stats you have in-game on that champion.
It will show that champions base stats without your runes/mastery.
Then, it will show the stats you have with the selected runes/mastery.
Then, it will show the total stats you will have in-game with the selected stats/mastery.
This way you don't have to wait till you're in game with your selected champion to see your stats and can help you with deciding what to buy to start off with.
It also would not hurt to display each champions different stats grow over-time during champion select and in-game. And certainly wouldn't hurt to show on the tool-tips what each abilities stat scale ratio's are.