Anyway adding proper support for TS sealed the deal for me - Svelte itself might never reach mainstream adoption but the idea of having a framework-compiler is something that I hope will, since it retains all the advantages of alternative approaches without introducing any significant disadvantages.
It might be worthwhile to frame it as "static and strongly¹ typed" with a footnote expanding on what "strongly" means to the svelte developers, just to get everyone to agree what we are even talking about in the first place.
I think the confusion around the term mainly arises from people in computer science having a strong ;) preference for binary definitions. To be able to say "X is strongly typed" and "Y is not strongly typed" is desirable.
However, linguistically, "strong" and "weak" are not binary terms. Static is: something is static or is not. But strength/weakness is an assessment on a scale. Defining something as "strong" is always, by definition, relative and somewhat subjective in nature.
That isn't to say that the definition of "strongly typed" is subjective; we can find agreement on what scale "strong types" live upon. But the application of the term to any given object is subjective. We cannot say "X is strongly typed", we can only say "X is more/less/very/not very strongly typed".
I agree with your overall argument, but in this conclusion I subtly disagree: it implies that we could come up with some linear quantitative scale from 0 to 1 of how strongly typed something is. I don't think we can, it's a composite of qualitative features that defies that approach.
It might even be a somewhat rock-paper-scissors like kind of thing where also we cannot really value each feature because their positive or negative value greatly depends on the presence or absence of other features.
Off the top of my head there's also "strong", as in "the type system is sound" or "not allowing pointer arithmetic".
It's not that clear cut.
Typescript is statically typed but it is also weakly typed. Types are validated at compile time, but they do not prevent you from using invalid types at runtime.