If it was fast, then the graphics could've been done better. Java is not good for gaming unless you're content with not going beyond subpar 3D graphics. Yes, there are commercial games made with Java, but they're only a few in number (at least on PCs). That's a telling sign that it's not meant for heavy duty games.
Slow compared to what? C++, C, Assembly? The JVM has come an awful long way in its 15+ years. And of course there are multiple vendors of JVMs now, all with different performance properties.
Minecraft is written in Java, and while it might not be that much to look at, a whole mass of computations are going on under the hood.
Programs written with the native code SDK still require a VM (for the Android OS at least), which defeats the purpose of writing in native code.
Not so much -- There's a native code SDK available too, which I'd make an educated guess is the preferred environment for pro game developers, for portability between PC and iOS if nothing else.
Multiple libraries that aren't well documented aren't very useful either. Many functions and classes are often so interlinked and esoteric that examples are required to know the proper use of them.
A simple, self-contained library that doesn't do what you want isn't very helpful, regardless of how well its documented or clear the code is.
So the best languages are the ones that act like nannies? I see that cognitive laziness and impulsiveness, but I agree with your point.
C++ simply doesn't make any over-reaching attempts to protect you from yourself. Java and many other modern, RAD-oriented languages have extensive guardrails in place, while C++ is happy to let you walk off the end of the pier; however, that does't change the fact that good design is required regardless of language or programming paradigm.
Though JS code is prone to hanging up because of bad loops or whatnot, it won't crash in the way that compiled programs do. With the recent addition of the canvas element, making games with decent 2D graphics is possible. It's a good alternative to flash, which has even worse performance issues.