Do keep in mind that it cuts both ways. Your travel times to the outside world are also your enemies travel times to your homeland. Just saying, not that you complain later.
99% of the travel being done to and from the isles will be by D'Harans. 99% of that 1% will likely be done by allies. Enemies are the least of my concerns.
In any case, I'm not asking "please give us shortcuts and make travel times shorter than one would expect them to be!" I'm willing to accept that the mechanics for sea travel will change for something which, overall, is better. I'm also able to accept that this will have, as a consequence, longer and more expensive travel times for D'Harans.
Because they make things more realistic, and are the same for everyone.
What bothers me is the shape of the sea zones in the central sea. Because they create distortions that are way larger than other probable sea routes (city to city travels, which will represent the bulk of all travel, with city to/from non-city taking almost all of the rest, leaving non-city to non-city travel with a marginal share of all sea travels). All I'm asking for is that the travel times per linear mile for Paisly/Port Raviel, Port Raviel/Port Nebel, and Qubel Lighthouse/Sallowtown be roughly the same as the travel times per linear miles for Candiels/Tower Fatmilak, Madina/Fissoa, Itau/Echiur, Dongheiwai/Flowrestown, Flowrestown/Poryatown, Askileon/Giask, Mimer/Libidizedd, Mimer/Eidulb, Libidizedd/Eidulb... All of these travel paths use sea zones with centroids about on the linear path between the two cities. Some of the other unmentioned connections have small distortions (which I'd love to see fixed if such was possible and I'm willing to draw proposals for such), but none anywhere as bad as D'Hara's distortions.
Travel times will necessarily increase. Travel costs will necessarily increase. I'm fine with that, they are the same for everyone, and will offer new mechanics and possibilities in compensation. And most of all, it's more realistic, and we'll finally be able to build that fleet we always imagined having. However, it's still a burden, it could at least be as imposing per distance traveled as others, even if it'll always be a lot more in total. (D'Harans will sail more than anyone, and almost only D'Harans will use these weird sea zones).
As I said, I'm offering to redraw it all for you. With a spreadsheet to give a report of the travel distortions in the new divisions. And I'd only add one more sea zone (splitting up Shattered Shores), though changes could also be done in the southern sea zones without creating any significant distortions should the total number of sea zones need to be the same (though I'm guessing remapping the connections would make the previous option easier).