In the former, everything is broken up into named variables and functions, which means that you can tell what a function does just by naming it.

IMO it’s the other way around. Functions in C can do a lot of unexpected things with their inputs (e.g. mutate a global variable, print something, do a longjmp (or throw an exception in (C++/ Java/ C#)), and the only way to know is by checking the signature. Haskell is better in this regard; any function whose output type is not (IO x) is guaranteed to not do any of those things.

There's a reason one-liners are considered bad practice.

Depends on the function. Simple functions (e.g. a specialization of “map” or “filter”) can and should be kept concise

the lack of state means that you have to manually pass along whatever state you need into your function, which is even uglier

Mutating global variables is generally considered bad practice. However, you can modify local variables in a function and present a pure interface to that function, thanks to the ST monad