You’re making the mistake of assuming the strategies you use for normal raiding would also apply to AW attacks. There’s nothing insensible or unjust about AW attacks, but (and this is kind of important) the Rules of the game are different: you have the extra Rule of the Revenge bar!
The reasoning behind the Revenge bar is that it gives the defenders the upper hand. The sense behind that is to throw a bone to all the beginner players. Because in AW they will be matched against much stronger players from the opposing alliance. And that would be massively unfair if it was done under the same rules as “normal” raiding. So the Revenge bar, believe it or not, is actually very just.
Reminder: the Revenge bar is active on your side as well, should an opposing alliance member choose to attack you.
So when attacking someone in AW, you’re going to have to deal with the Revenge bar as well. You know it fires more often the less heroes on the defence team are standing? I recommend browsing some of the threads about AW for tips and tricks. @Dante2377’s thread here Dante's Alliance Wars Primer (with Video from Beta) - #2 by Dante2377 has some valuable pointers. Hint: if you’re stretching out the fight over a long period of time and/or do not have healing capacity to deal with revenge damage, you’re likely not doing it right.