Not supporting bashing language in this thread, but this was a reason I never wanted to develop in Java. This terrible desktop experience created a notable bias towards Java, and only later I learned that it's not that slow for networking services (but it was too late).

This terrible desktop experience was created by developers that didn't bother to learn Swing before they jumped into the keyboard.

Writing everything on the main UI thread, not enabling system L&F, reading books like "Filthy Rich Clients", adopting third party Swing components with modern L&F....

I suggest you check out JavaFX. It is a mature, modern, flexible UI library that is now considered the standard.

But of course, bad programmers make bad apps, no matter how good the ecosystem is.

I've found that terrible performing Java apps were created by terrible performing engineers.

Java, from my experience, has always been quick and flexible.