There are like a thousand little details a type system has, and you focus on one thing, the existence of null for .NET interop, and decide this means the type system can't be overall better?
F# lacks functors, first class modules, row polymorphism, GADTs, PPX extensions, and likely some others I'm not aware of. GADTs, row polymorphism, and PPX extensions I've wished for in particular because they solve some problems I frequently run into with MVU/Elmish architecture on the front end.
F# instead has inline functions with static constraints (similar to C++ templates), type providers, computation expressions, and units of measure.