She seems content on just blaming Java itself, rather than blaming her lack of Java understanding. There is a reason Java is used in high end projects like Chemistry software, it's really good at managing data.
Honestly, the very first thing I don't get about her architecture is why it even uses nested Javascript, I mean the whole Webview thing.
I'm trying to make my own prototype of the game in this genre, and after experimenting with JavaFX I understood that this approach of JavaFX Webview by mixing Java and HTML/Javascript is weird imo. Like, if you wanna use html/js stack as they do, then do everything in js/ts, maybe with any suitable framework, and deploy either directly in the browser or as an app with Electron.
Otherwise, there are a couple of libraries for Java for game development. For example, there's FXGL, a superset of JavaFX designed to make games. Or the one I use, LibGDX, which I think is so good compared to plain Java/JavaFX as it has many community libraries, like a couple of ECS libraries, and cool libs for text formatting.
Don't get me wrong, they can choose whatever architecture design they wish, it's totally up to them, but when I simply tried to run a debugger to see how the game works, I was a little confused, and then after I saw that most classes thousands of lines, and some are 10k+, like GameCharacter a 30k, I got even more confused - how do they even navigate over all of that... maintaining such code base is probably uneasy thing to do ngl.