The acrop is well defended because it is the most important part of the defense. It maximizes the stables and garrisons production. As you saw every one of my stables and garrisons are within the influence of my acrop and all are spread out in a relatively even arch. This base will spam defensive troops faster with the acrop lasting longer than any other base design without it.
Spamming troops does more than just do damage to enemy troops. They also delay attacking troops, preventing more damage from happening to buildings. Spamming troops, in my opinion is also the most effective way to defend your base for two reasons
1. Cavalry is very popular, particularly because of the DPs increase they have received. Cavalry goes after defensive buildings so the more defensive troops you can create to distract them from doing what they do allows your defensive buildings to do what THEY do.
2. The Romans unique unit gets a bonus against buildings but not against defensive troops. Why does this matter? Have you noticed how many Romans there are, especially
since the ability to change nations was introduced.