Once the runtime is bundled in, what does the size of the standalone application come in at? Curious if it is close that of a bare Electron app (around 50-90 MB, depending on the platform).
Note that even in 8 you can do a DCE pass over the code and erase files you know you won't need from the JRE image by hand. I did this and shrank the size of the download by about half. The JavaScript world calls this "tree shaking", you can use ProGuard to do it in Java but it's a bit fiddly to set up.