In terms of island shape, I do like how diverse it is. You can see where islands may have once been connected which is a nice touch. It all feels a little flat though, and I'd love to see more detail added, like you did here: zacherygangrel.deviantart.com/…
You are correct, it does have a flatness to it, but that is not without intent, although perhaps more so than first expected. I do have another version with kingdom borders which adds a bit of detail, but that details also hides the landscape in many ways. Thank you very much for commenting!
The flourishes were made in Illustrator. They were stock vectors I had purchased a long time ago, I cannot seem to find a link to the original vectors I purchased but I believe I got them from Shutterstock
Aside from that I cut them up a bit, Stretched out the straight lines, pasted it into PS and finally added a layer style. Simple. I just added it as quite border and wanted to be different than my standard borders. Thanks for asking