About multi in it:
What about basing the multis for each team on how many flags have been capped?
Defense starts with x5, attackers with x1.
First flag get captured and Defense gets x4 and attackers x2.
Continue like that.
This way, there's actually a reason for attackers to never give up. After 15 minutes of a round, if the first flags weren't down there was no way for attackers to completely win so everyone on attacker side that didn't have a multi usually left. Teams got balanced and same thing happened again. With a "dynamic" multi through the round it means theres never a reason to give up. Defenders still got a reason to keep fighting for their x2/x3, while attackers can at least get some x2/x3 on a round they are already losing.
Ofc, what to do with rewards for winning/valour? I guess some sort of bonus XP/Gold for a win/valour, but that's not a perfect solution.