So in other words, at TH9, I should upgrade ATs and Xbows last to keep my match rank down?
Absolutely
When you go up a town hall, this is what you want your update progression to look like (just personal opinion, also only including building that deal with war rank):
1. Troops- if you're bringing max TH9 defenses into your war rank and max TH10 troops in for your attack, you're attacking power is above your defensive weight, huge advantage in war.
2. Traps- this one is simple, low rank and the defense cant see that they are maxed. Bombs help with hogs and balloons with air attacks.
3. Walls- easy to upgrade with gold while increasing troop level. I pair my troops/walls at the beginning of a TH phase
4. Teslas- not sure what they carry as far as weight but they are the strongest DPS defense in the game and opponents cant factor them into their attack since they are hidden.
5. Archer Towers- one of the best defenses at higher levels
6. Sweeper- low war weight
7. Air Defense- you're gonna get lavalooned a lot
8. Cannons- do decent damage vs GoWiPe and GoWiWi
9. Wizard- not as useful due to lack of barching in high levels
10. Mortars- see above
11. Inferno- by this point your troops should be maxed and walls looking good
12. Xbow- worst defense in the game
Again, just my personal opinions