So you're focusing on the memory model. To which I'll say, it's not the language but it's the _machines_ that have SMP so effects will be visible out of order. The machines provide you with escape hooks to serialize read and write effects, and the language
must give you access to these hooks because if the language opts to keep up the illusion of all sequential effects even in the face of SMP, it has to do so by serializing basically all memory accesses, which is going to be incredibly slow.
That code doesn't appear to be sequential from other threads is not the language's fault. It's just a fact of reality.
If you don't want to do SMP / lock-free programming, you don't have to pay for the complexity. You can still write "sequential programs" like it's K&R. Don't do multiple threads, and you don't have to care. You can also do multiple threads but use mutexes for synchronisation, everything will be fine.
Pretty much nobody uses restrict or volatile. There is some fringe stuff that is obsolete and maybe badly designed, but by and large you don't have to use it or interact with it. Compare this to other languages / ecosystems which have this amount of cruft times 100.
It's still this language where you can define a struct, then define a function that receives a pointer to the struct, and it does as you say, and you can actually read and understand the code a month later.
If you need to go fancy for a reason or another (most likely a bad reason), you can do that too, and of course you'll have to pay for it. But most likely, the complexity is not "cancerous" -- define a simple function interface with the most basic assumptions you require, and the complexity is pretty much isolated behind a simple pointer to an opaque structure.
> So C11 definitely isn't the simple language for a 1970s computer any more. C11 is a competitor with C++ or today Rust. And it doesn't fare so well by that comparison.
That's ridiculous and you know it.