What makes AOE better than other RTS games is the counter system. For example calv beats archer, archer beats spear, spear beats calv. It’s not just a race to make an army, but you have to think about when to make which unit then micro them in battle. This principle is not extended to the water in any of the AOE installments. This makes water games quite lame. To paraphrase a recent Hera comment “water fights are just if my ship beats your ship than I win.”
I think every civ should have three basic warship types that counter each other. We already have Galleys (or civ equivalent) and Demo Ships so just one more should complete the triangle. Suppose we add Boarding Ships that grapple a nearby ship and either slowly destroy it to make it easy, or it captures the ship and leaves it at 1/4 health to make it realistic. With this, Galleys beat Demo Ships because of their low armor, Demo Ships beat Boarding Ships because they are cheaper, and Boarding Ships beat Galleys. Obviously, civs would have their own versions, like the Chinese Junk would be a cheap and fast Galley equivalent. Also, some civs could have special ships that would fit into this triangle without breaking it, like say a Byzantine Fire Ship that, like the demo ship, does well against Boarding Ships but fails against Galleys. Just, it does not fail against Galleys as bad as a Demo Ship would.
The other problem with all AOE games is that once your navy is destroyed, it’s hard to rebuild it without having it get picked off. To solve this, I suggest every civ have a Sea Tower that, like the Dock, can only be built on the coastline. It has more range than a normal tower, and does extra damage to ships. But is quite useless against land targets. This would allow a safe area to rebuild your navy. It would out-range all enemy ships until they get to the Imperial Age and make the Bombard ships which would be its counter.
What if there was a fourth type of ship that every civ had that shot ballistas, and the galley line only shot arrows even after upgrades. This other ship would fire at longer range and would be the glass cannon that you try to protect behind your main line of ships. This would make navel battles even more dynamic.
Best of all, for all the land map only people, this should not ruin anything on your end