I'm not a latex expert. I don't know what the difference is between tex math, latex math and amsmath is. (And please don't explain it, I don't care.) Maybe there are some weird expressions out there that don't have a typst equivalent, if we really looked for them. But I haven't run into anything myself, despite writing a pretty math-heavy CS paper. (Or at least, the early drafts were math heavy.)

> I'm not interested in a programming language (though naturally being able to write plugins would be useful ala luatex), but a textual macro system.

Are you sure? Because latex macros like that are really horrible to read & write, and latex gives you notoriously hard to read error messages for your trouble. Here's the equivalent in typst:

    #let dt(x) = $(∂#x) / (∂t)$

In my opinion, this is way more readable. That code defines a lambda function (like arrow functions in javascript) that returns a "math mode" block ($this is a math block$). #x escapes the math block to evaluate x - which is just the function parameter we defined earlier.

And you'd use it simply:

    The result is $dt(y)$

Its not a macro system. Its just a function that you can call anywhere - including from other functions. And the function returns a block. I personally think its much nicer, and more familiar than the latex macro equivalent.