I need it to be a first-class feature because I’m a baby. My #1 complaint with C++ is that they make everything a lower-class feature to avoid breaking backwards compatibility and it makes the language more verbose, less enjoyable, and less intuitive.
All that said, I’m personally okay with the decision to omit typeclasses since the language is meant to compete with C, not C++.
I think Zig competes with C++, too. But to match the expressivity of C++ you don't necessarily need to have the exact same features. C++ gives you control over generics with concepts, and Zig does it differently -- with introspection, which is very much a first-class feature. If Zig wanted to achieve what other languages do in the same way they do it, it wouldn't be radical. Instead, it offers a different way. When comparing two languages, especially those designed with drastically different aesthetics, you don't ask how easily can an expression in one language be translated to the other, but how easy it is to achieve similar general goals.
I think Zig competes with a school of C++ that tries to stick to a simpler, limited subset of C++. Games is one area where C++ is much more common than C, but also where a lot of C++ practices (exceptions, excessive template use, many parts of the stdlib) are discouraged and things tend to be kept "simpler".
I'm sure there are a good handful of other fields that currently write "minimal C-like C++" and I think Zig competes with C++ in those cases.
But Zig has counterparts to exceptions, templates and anything you may want to do with them; it compares quite nicely with even "rich" C++. The one thing it intentionally doesn't have is operator overloading. In general, I'd say that the difference between Zig and C++ is that when you do some clever stuff in Zig, you need to be explicit about it so that the reader knows this call-site uses dynamic dispatch or that there is a destructor being called or that this operation isn't really the standard +.
