Svelte is a bad example. They have roughly identical type checking before and after that switch. The switch is mostly just an aesthetic preference for one syntax over another and an ideological stance about being able to run code directly in a browser without a build step.
It's not an "aesthetic preference"; it's a functional preference for debugging and iteration speed as cited by the team.
Fair enough. Perhaps what I mean is that they don’t have a strong aesthetic opposition to JSDoc, which is presumably rare among TypeScript developers.
This is why I prefer to stick with JS and JSDoc.
I have been doing pro webdev since 1995 and since I got my initial experience without all of the contemporary tooling, my process has evolved to require very rapid iteration: the delay of a compile step can often break my concentration and prevent a flow state.
Which is quite hypocritical coming from a compiling framework and thus such a ridiculous stance.
We hate build steps in our build step.