> It just doesn't seem like that big of a problem.

It really, really depends on the codebase. There are absolute mammoth tire fire codebases out there - particularly in "enterprise code". These are often made up of insane hierarchies of classes which in practice do nothing but obscure where any of the actual logic lives for your program. AbstractFactoryBuilderImpl. Wild goose chases where you need some bizzaire and fragile incantation to actually create an object, because every class somehow references every other class. And you can't instantiate anything without instantiating everything else first.

If you haven't seen it in your career yet (or at all), you are lucky. But I promise you, hell is programmed by mediocre teams working in java.

I've seen such difficult to follow code in Java, and I complain about it every time. But having multiple inheritance isn't the cause (because Java doesn't have that). Nor does having multiple interfaces with default implementations have any real impact (at least in _any_ case I've seen).

The only real difference I see between multiple inheritance and multiple interfaces with default implementations is constructors. And they can be handled in the same way as default implementations; requiring specific usage/ordering.