Well it is. You won't discover how deep the rabbit hole goes with that type until you start trying to debug it. For example, try fixing this issue which is the result of a problem with that type:
Interesting, I wonder how much of that is due to poor implementation by the authors vs. issues with TS vs. issues inherent to building a typed language on top of the mess that is JavaScript?
Most languages with strong type systems (I'm thinking at least as strong as Java or C#, maybe stronger) wouldn't have those same sort of footguns. In C# I've run into other kinds of fun nightmares with types, like trying to use interfaces with Entity Framework Core. But I think that's more EF Core's fault than C#'s.
From skimming it for about a minute it seems like it's just a strongly typed way to generate HTTP requests? It really doesn't look too complicated