I'm trying to work out in my head if it helps the true challenge of programming - not writing the program in the first place, but maintaining it as requirements evolve.

The examples for functional programming benefits always seem to boil down to composable functions operating on lists of stuff where the shape has to be the same or you convert between shapes as you go.

It's very useful, but it's not a whole programme - unless you have some simple server side data processing pipeline - and I'd argue those aren't difficult program.

Programming get's difficult when you have to manage state - so I accept that parts that don't have to do that are therefore much simplier, however you have just moved the problem, not solved it.

And you say you've moved it to the edge of the program - that's fine with a simple in->function-> out, but in the case of a GUI isn't state is at the core of the program?

In that case isn't something with a central model that receives and emits events, easier to reason over and mutate?