Garrison effects are pretty problematic for ships. Previously, ships subscribed to the "bigger = better" model, and 1) having a ton of ships and 2) garrisoning ships was the way to dominate the seas. But this takes an absurd amount of population, so very few players wanted to play like this as there is usually land to fight over.
With garrisons affecting the strength of ships, you often could not tell how strong an enemy ship was until after it sank your ship with your handful of soldiers inside.
On improvements we can make, I think moving scout ships to p1 would be good. I initially was against it, but I think its the right move. They might need to be weakened a little bit.
What cost changes would be good?
I heard that ships are a bit weak to land units, so we could bring up pierce armor.
I don't think the techs are very complicated, but if players don't get a lot of the techs and don't get value out of the techs compared to just making additional ships, they should be streamlined.