But, IMO, therein lies the value-add of dynamic languages: You can always impose static strictness on a dynamic system - the other way, not necessarily so easy.
That’s right. But everything is parallel. They can make types as loose as they want, e.g., use Strings for everything.
Dynamic: Loose now —> Strict later
Static: Strict now —> Loose later
Where later usually means never.
It sometimes feels that way 
Eric