I don't think they were. Static type systems can greatly hinder FP. Or to be more specific, language semantics and runtime behavior (encoded by the type system

I don't think they were. Static type systems can greatly hinder FP. Or to be more specific, language semantics and runtime behavior (encoded by the type system) can influence how powerful your FP is - and by "powerful", I mean how much boiler plate you need and how much you can generalize things. So yes, having certain characteristics of type systems do help with FP while not being core to FP. It can certainly make things more pleasant though.