Way to make Diana more balanced

Ever since the assassin update Diana hasn't really had a strategic niche. There's nothing that she does better than the other AP assassins, skirmishers or divers. I hope that they are targeting her for the diver class update but in the meantime I want to propose a buff that I think will make her relevant but not overpowered. All I want is for her W cooldown to decrease by 1 second every rank. That's it. Currently her W cooldown is 10 seconds and isn't reduced by rank. This buff would give her a 6 second cooldown at rank 5. By giving her this buff it gives a possible incentive to max W first in difficult matchups (like Jarvan does) and it allows Diana to team fight better in the late game because it allows her to potentially get a second shield if she plays things well. Right now its near impossible for Diana to survive long enough for her shield to come off cooldown (unless she builds bruiser) which make it very difficult for her to excel in the late game. This would give Diana a strategic niche to be a slightly tankier alternative to other AP assassins, skirmishers and divers (though lacking any method of escape.)