How is paramerization of types on values not a typesystem-level property ? There's definitely nothing akin to macro expansion involved since you can do type-level computations that way

I’m pretty sure the implication is that since template instances are made specific at compile time and are done so in a way that is very analogous to AST based macro expansion. Specifically, C++ templates are a programming language which runs during the compilation of C++ code that acts by producing valid C++ AST components.

I have never seen a definition of type system which cares about things being done at compile-time or runtime, or that there even is a compile-time or run-time

Never heard of static vs dynamic type checks ?

Expressiveness of type systems is about which types (and thus type checks) you can express, not when the type checking occurs