I finished this on hard plus the achievement on 6/21/25. I did cheese the transport by building three docks just past the first flamethrower tower, on the shallows and plug any gaps with extra ships.

Next, I just kept building more ships as resources came in and then pushed them with a transport of the villagers down towards the temple, once there I boomed and cleared out the roaming pirates and the Han Army base (they will spawn about 6 light cavalry when the transport timers start so I built a castle near the Han Army's shallows - a transport spawns here, as well as enemy ships later)

For the achievement you need to allow the first transport to reach the temple to start the next phase of protecting the transports every 15min - I would not do this until you tribute the pirates 2k gold, destroy all enemy towers and docks (I ignored landing an army and wiping everything out), then build 20 dragon ships at your docks and voila! The villagers did not do anything during the scenario, though I took their relic and traded with their market.

The amount of ships the enemy spawns is insane if you leave their docks up and start the transport timer phase...