[Epskampie]

Verbose? Do not agree at all. Adding types to function parameters for example is just a simple ": TYPE" I do not see how that could be much shorter.

Furthermore, where possible (variable assignment, function returns) types are inferred, and do not need to be specified at all, leaving you with mostly plain JS syntax.

[verttii]

No algebraic data types leads to having to add an additional discriminating union type key.

Besides that, no type signatures without parameters and other things just produce a lot more code than you'd have in a nicer type system.