There are 10 emblem types, so any player will optimally have 10 heroes emblemed up. However war uses 30 heroes (6 attacks of teams of 5) so realistically 4 of those attacks will be unemblemed heroes vs the defenders absolute 5 best maxed out emblemed heroes.
War defenses (WD = field aid / arrow attack / attack boost) are supposed to even things up since a human controlled attacker is always at advantage vs AI defenders. However this disparity is made up for with emblems.
I propose that war defenses are only ON for first 2 attacks, and are OFF for the remaining 4 attacks.
WD will be OFF if the total Team Power (TP) of the defending team is either 10% more than the attacking team, or 500 TP more (since emblems add 5 power each, an emblembed team can be up to 500 higher TP).
It would be easy to implement, simply have an indicator showing if WD are ON or OFF and will be based on the TP of the attacking team vs the defending teams TP (very clearly indicated on the screen just before you confirm whether or not your going to attack).
Example, if attacking with a team thats 3000 TP, defenses will be ON when attacking a team of 3300 TP or below (or 3500 depending on what they decide to go with) but if attacking a team of say 3600 TP with your 3000 TP team, the war defenses will be OFF.
War defenses can only be off a max of 4 times in a war, so you will still have 2 attacks with WD on (if you have only 2 attacks left and strategically planned it so the first 4 were all WD off, then these last two will be ON regardless of TP).