In much the same way as "being Turing complete means you can do anything", it just being possible to do compile-time execution isn't the reason Zig is exciting here.

C++ adding the same features means it'll be possible, but it has a much larger intersection of alternative features to introduce edge cases with, and _many_ implementations that will have this feature with varying quirks: all of this means C++ will have to do a _much_ better job than Zig does here to achieve nearly the same result.