Edit: And actually, I don't see how that situation is any different if you use one way of looking at it or the other? In "your way" the player cost 5 million each year for the first 4 years, in "my way" the player cost 20 million in total for the 10 years.
Yes....but your method concludes that buying the player for ?ú20 million and releasing him for nothing represents a ?ú20 million loss regardless of what has occurred in the intervening ten years. It fails to take into account what the player has done at the club - what he was bought to do.