[iLemming]

> most of them are dynamically typed (thus don't need sum types, as there are no types)

I think you're conflating. "No compile type checking" and "no sum types" are different things. Sum types are about modeling data as "one of these variants". You can do that in any language - the difference is whether the compiler enforces exhaustive handling or not. Clojure (for example) absolutely has the equivalent of sum types, just expressed idiomatically rather than enforced by a compiler - multimethods, keywors as tags or tuple vectors can be used as represenation of tagged unions. Malli and Spec both provide sum types with validation (it just happens runtime).