Well. I'd be upset if custom operator==() for plain-old-data structs was removed from C++, but Java never had it to begin with, so for Java, it just means that you have to fall back to using traditional classes (or compare using something other than ==) if you need such "fancy" features.

Java can also distinguish a 2/3 object from a 4/6 object using == when they are not value types. It can even distinguish a 2/3 object from a different 2/3 object.

> There’s nothing wrong with having non-normalized representations

There is a lot wrong with that: complexity, bloat, and slowness.

> But now client code can distinguish 2/3 from 4/6 using ==

That's a great way to obfuscate code. Not a good idea. The right way to do the comparison is, just make a function called CompareRational().