> If you have to rely on what is effectively a linter to type-check for you to make sure your program won't do surprising things, that's not an incredibly positive indictment of dynamic languages as a whole.

Using TS or Flow definitely goes beyond what linters accomplish. That being said, your criteria for language quality sounds squarely-rooted in Static typing. Dynamic languages trade upfront taxonomic activity for rapid prototyping and then you come back post-prototype to analyze and ensure correctness. It's just a different approach. There are tradeoffs both ways.