The global namespace in typst is limited to "states", a rather specific feature similar to the global TeX counters for headings and equations. So it's possible for two packages to increment the same counter. Everything else is local. All functions and variable definitions are local, and every function is pure: a function call cannot have any side effect. In particular, a package cannot redefine a function.
(You may wonder how functions can be pure if they can increment counters.... The way it works is that you call the function and put the return value in the stream of content of the document. And this value can be something that says "increase counter X by Y". And when you read the counter, typst applies all such "counter instructions" that are in the document so far, and gives you the result.)
The special knobs that typst provides are the "set" and "show" rules. With "set" rules you can change the default values of elements created later in the same scope. For example "#set text(fill: red)" will make it so that all text created later in the same block of code without a specified color will be red. With "show" rules you can define transformations that will be applied to elements created later in the same scope. For example "#show math.equation: it => figure(it, caption: "An equation")" will wrap every equation in a figure with the given caption.
I think the main reason LaTeX is a pile of cards is because TeX is terrible as a general purpose programming language. Just an example: the fact that a macro called with particular arguments will behave differently depending on the current state of catcodes is a craziness that's hard to imagine when you think in terms of "normal" programming. And the whole ecosystem of amazing packages that make LaTeX so useful, they need to do the kind of things you'd normally do in a normal programming language, so these packages end up working around the oddities of TeX in ways that make the whole thing a pile of cards.
With its design based on pure functions, I'd say typst is at the other end of the spectrum in terms of how easy it is to write code that works reliably without interference from other people's code.