Ok, first of all, get rid of all your towers and replacd them with forges or guilds. Towers are a waste of lands at your size.
Another question would be: Are you at max ally bonus plunder? At your size, I roughly estimate that you'd need around 2b in allies.
And yes, Owen has another valid point. To maximize your gain, you'd have to skim your troops and spies.
Another thought: equal number of actions doesn't mean those are the same actions. Maybe you threw items in item phases and your mate didn't? Or vice versa?
Start with selling those towers...