Respectfully, I think you're throwing the baby out with the bathwater.

I read your story, and I can certainly empathize.

But just because someone has made a tangled web using inheritance doesn't mean inheritance itself is to blame. Show me someone doing something stupid with inheritance and I can demonstrate the same stupidity with composition.

I mean, base classes should not be operating on derived class objects outside of the base class interface, like ever. That's just poorly architected code no matter which way you slice it. But just like Dijkstra railing against goto, there is a time and a place for (measured, intelligent & appropriate) use.

Even the Linux kernel uses subclassing extensively. Sometimes Struct B really is a Struct A, just with some extra bits. You shouldn't have to duplicate code or nest structures to attain those ergonomics.

Anything can lead to a rube-goldberg mess if not handled with some common sense.