While this is true, static type checks do even less for this problem. Do you even create specific types for value ranges eg IntegerBetweenZeroAnd100? You're in a vast minority if so, and I'd be interested to see how tedious it is to construct all these non-native types everywhere.
> If you omit manual type checking in your code or in the respective unit test, you may miss some subtle failure scenarios.
There's generally not much that's subtle about a wrong type. If the code is executed at all, it will usually blow up. In my experience, the subtlety comes in the values.
> I personally find that type safety cuts down the number of unit tests I write by half
I just don't buy this (but then again my team goes for near total coverage). Nowhere near 50% of our tests are testing anything that would be solved by static types.