At later Ages he will go down .
Seeing as tank depot upgrade costs 7 mil gold , and one wall piece 3 or 4 mil gold it is natural.
Two wall pieces won't impact your rating as much as upgrade of defenders from cuirassiers to tanks. Even upgrading 4 or 10 of walls won't
Some upgrades as Bunkers or upgrade from Stables to Tank Depot have very huge impact on your war rank.
Why is that ?
Upgrade 1 Stable (availble cuirassiers to be spawned at the same time on map from 1 Stable ammount to 30 troop space) to Tank Depots (avalble tanks on map at the same time from 1 Tank Depots ammounts to 40 troop space) and you have huge defensive boost of 10 troop space more from one Tank Depot.
Upgrade 3 of them and you get 30 worth of troop space more. With range of 3 , not 1 as cuirassiers had.
Build one bunker and you can have 50, or 48 troop space (depending on if you have library research that decreases Htank troop space by 1) of worth of troops on map at the same time since bunker can spawn max 2 of Htanks.
Garisson upgrade at IA has more impact than upgrading walls too.
Why?
Because your defenders spawning from them get more by 0,5 range .
It isn't much maybe, but they can shoot attackers through walls and that means their survivability is better,and that has huge impact in your base defending power.
Hope you get what I'm hinting.