In a particularly constrained and archaic language like C, it may be clearer. In a modern language, in no way is subtraction of an offset clearer and simpler than almost any alternative. Even in C, as you've mentioned elsewhere, you've had to use macros to make it at all clear, and macros can do anything and are inherently opaque.

Many other languages also have newer/different approaches to solve some of these problems, be they subclassing, generics, macros, JITs, or other. They mostly cannot do this as efficiently, but that seems less like a clarity/complexity concern and more like a low-level-programming concern.

> How do you get from the child to the parent in, say Java?

In Java, you do indeed have to embed mutual pointers and just be careful. As a C user, you must be used to being careful. Even C#, which does allow structs, doesn't have references-to-members that can be turned into references-to-owners. However, there are patterns and language features that people use to handle similar things, like subclassing (for lists) and generics.

> How do you copy an object that holds, say 4 vec4, vec4 being a struct that itself 4 holds floats?

Copying structs as a block works fine in Rust, C++ and C#, along with many other languages. Again, Java is a little more limited in this regard, though I believe they are working on adding value types.