Interesting. I think you should ask some questions inside the Svelte discord channel. My opinion is that Svelte is the easiest to integrate because it doesn't require the runtime that react does, for example. I've got Svelte running inside lots of non standard places, like browser extensions (https://addons.mozilla.org/en-US/firefox/addon/please-at-me/). It can take a few minutes to figure out how to get it built correctly for the context but it has never blocked me.

I don't disagree about your typescript point. Svelte community seems to have aligned around typescript being a challenge and I do like their assertion that jsdoc+eslint is a better approach.