Lots of insults, but the difference here is that I know exactly how to do what you're doing in C, but it doesn't seem like you ever tried out modern C++.
How hard is it to understand that to get a class definition, all the stuff that's used inside the class, including declarations of internals like private fields and methods, needs to be included first? How hard is it?
This is a matter of dependencies and if your dependencies are simple definitions too it isn't going to matter. You are going to have to have definitions of your structs and functions in C too. A data structure without dependencies in C++ is no different than a data structure without dependencies in C. This isn't a language issue and has nothing to do with destructors.
without insane C++ classes and features.
It isn't destructors that cause long build times, if it was you could prove it. I said this multiple times but you're mixing a bunch of stuff together because you know staying on topic doesn't match what you're upset about.
I'm talking about systemic problems, which manifest in lots of ways
You didn't give any explanation of these, you just made a lot of claims. You still seem to think claiming something with no explanation is evidence. A kid saying they run fast over and over doesn't prove anything, you have to show it.
You haven't got a clue what you're talking about.
They are both forward declarations which I avoid like the plague for all the reasons I outlined before. Your whole schtick is that you want forward declarations and don't care about all the ownership and value semantics that save you from 50 years of C bugs.
There is no "like every other value" in C++, regardless of how hard people are trying, and regardless of how much complexity these people pile on top of this language.
Another claim without evidence. Make a value, it goes out of scope. Make an 'object' data structure, it goes out of scope. Move it if you need to, so simple!
which you can simply copy as bytes.
Copy constructors do this if you need them to. You can't just use plain structs with static sized arrays for everything, at some point you need to make real data structures that use the heap and then you will need to manage their memory. It could be automated for you but you might have to be a little more open minded.