I use FASM, and FASM has probably one of the most powerfull macro languages out there. FASM actually implements _only_ this macro language and _not_ the x86_64 assembler itself. The x86_64 assembler is actually written using this macro language, like the support of ELF, COFF, etc, binary formats. Some ppl have implemented an ARM assembler with this macro language (and I am thinkink about RISC-V). Its author likes to refer to this macro language as an "assembler writting toolkit" which looks to me more than fair.
As a practical example, this macro language has full support of modular and hierarchical namespaces. I found myself lost into dividing my code paths in basillions of namespaces and that way too much. Excessively, I also started to write my "own" language using this macro language: I was not writting assembly anymore, only macros and some with hardly any assembly in them.
This is actually a bias that happens with any computer language: the tendency of devs to "maximize" the usage of some syntax, which kind of increase exponentially with this very syntax complexity, to reach a point where a Rube Goldberg machine looks efficient and sane (yes, this is severe irony).
