Agree.
Also, I had a situation when I was supplying 5 fishes[Slot1], 5 schnapps[Slot2], 5 work clothes[Slot3] from island 1 to island 2.
Because Iam unable to set something like:
"Only load if there is less than X on island 1"
or also:
"Only load if there is less than X on island 2".
(at least one of the two...but both would be nice to have)
What would eventually happen is that the fish storage would get full first on the Island 2, so the ship would end up filling all the other slots (for some reason) with like 3 Fish[Slot1], 4 Fish[Slot2], 5 Fish[Slot3]...trying to empty them when it can. Meanwhile being unable to move the other things.
Not to mention that it is also starving the Island 1, because there are no limits like the OP mentions.
This definitely needs something added.