Which of those is more beneficial indeed remains to be seen and might end up being purely a matter of personal taste; the very thing you call a downside I see as an upside. I think that talking about the positives "consistency and cohesion" where composing primitives works as a positive is merely a matter of habit. Zig treats some aspects that other languages sees as primitives as if they were any other part of the language, where code and libraries rule rather than a growing collection of primitives. I do agree that in principle a language could be too unstructured for some domains (Lisp?) but interestingly, Zig didn't go as far as syntax macros, whereas Rust did. Anyway, Zig finds a surprising middle-ground that is, as yet, hard to definitively judge, whereas Rust, for better or worse, is more of the same.
I was thinking of The Lisp Curse[1] while reading your comment and then you mentioned the language! I’m quite excited by Zig (even if safety is lower priority for it than for Rust, it is really pushing the tooling envelope) but I do wonder whether the “anti-composition hypothesis” here holds up for relevant projects today. Many C programs include shims for compatibility between multiple different “library object models” (hell even strings count here) and they seem to be a common source of security and performance issues. Maybe in the domains where Zig is most competitive that dynamic won’t play out? Or maybe comptime provides tools that will still enable composition or at least allow for lower overhead “object model shims”? I suspect that it will be hard to know more about how it plays out until there is more language stability and code sharing, maybe even a repository like npm or crates.io.
Can the "safety is lower priority than rust" trend stop? Zig is not less concerned with safety and will catch illegal behaviour at runtime for that which isn't caught at compile-time. It's only ReleaseSmall and ReleaseFast that elide this where you're able to toggle safety checks via a builtin if you wish. There's ongoing work to provide more of it within the standard library with the GeneralPurposeAllocator being an example of it.
I'm not suggesting that Zig isn't concerned with safety, but it's not a language designed first and foremost to offer certain safety properties. For Rust you can say "as long as you don't write the `unsafe` keyword in Rust, you'll never introduce memory or thread unsafety". Is there an equivalent for Zig? Not AFAIK but I'd actually be quite happy to be shown wrong.
I would put it differently. Rust sacrifices anything -- including things that may hurt other aspects of correctness -- to soundly guarantee (assuming the compiler is correct) no undefined behaviour in its safe subset (and yet makes some concessions, as a large percentage of Rust programs do employ unsafe code, and so don't make such a strong guarantee), while Zig finds a different balance, at times sacrificing possible UB for the sake of helping with functional correctness. Even if you look at correctness only, it is unclear which approach, if any, offers a better story.
