What are you using to kill the shogun and destroy a level 4 gate in 3 minutes ? The best way I found was to don't upgrade the leadership (level 3 at the beginning for me) send zato (I have 30 leadership points at the beginning) and then send "horse archers" for the shogun. I use my bow to attack the shogun but I have to avoid his sword. When he died I send a lot of assassins to destroy the gate but I usually don't have enough time.
I have all the allies unless the sword master and I have upgraded them to the best level without using gemms/glucoins.
Sorry for my bad English.