> is to create a functional mini-DSL

Exactly. Is there a formal term for this?

Instead of one gigantic function with 50 parameters, you have 100 "template" functions, that all make use 60 different "helper" functions (what you're calling the DSL).

Instead of castles-of-logic abstraction, it's nuts-and-bolts or grass-roots abstractions. I've never come across a name for this development style.

But it generally works extremely well when building processes for tens/hundreds of data formats or customers or what have you.