> The hardcore “sound types” crowd believes that anybody using dynamic types is doomed.

What they believe is that "dynamic types" is a misnomer, and if you think your program is checking dynamic types, it is in fact doing runtime pattern matching over a variant record. There's nothing wrong with pattern matching and variant records; but conflating them with types is just nutty, and using them pervasively as part of the ordinary flow of code is no different than programming in old-style VB.