Well I don't agree with static attributes, but I would like they to have a limit if how much they improve, for example to have 99 Speed you should begin with at least 80 Speed, and even with that it should be hard to reach 99. If you begin with 25 Power your max limit should be 50, there are others that could increase more like P. Vision, Discipline, BR Ability. Durability is a tricky one, because sometimes players are very healthy athletes, then they suffer some big injury and they never recover their durability again or sometimes they do.