An idealized dynamic strong typed language can actually give you the guarantee that all statically valid programs give you well-defined runtime behavior. This is a huge advantage over weakly typed languages that you also get out of the idealized static typed language.

The issue is, outside of languages with very baroque type systems or monstrosities like Java's sandbox, static typing often winds up decaying into weak typing, which offer much weaker behavior guarantees than real-world dynamic languages.