Thanks for the feedback!
I'm surprised you didn't see any pirates. There's a 10% chance any ship will be one, so if you play for a while it's practically inevitable you'll see them. I usually start seeing them no later than about a minute in.
I generally agree with your thoughts on the gameplay loop missing something. I'm not sure how long you played but eventually with the number of ships (and wrecks) increasing it goes from a slow-paced traffic management game to a more fast-paced game about triage. But this system is only really good for one playthrough and entirely depends on people liking the slower paced portion at the beginning. I wanted to do more with the rescue ship. Some of my ideas were to give it a max-occupancy where once it rescues enough ships you have to guide it to a harbour to offload their crews, or to have a unique rescue ship spawn per wrecked ship that you would need to guide to and from its specific wreck. I had also considered adding more obstacles like icebergs that would aimlessly float around the water. Unfortunately I didn't have a lot of time over the week to work on this, so I wasn't really able to experiment with these ideas.