And if you're expressing hierarchical UI, the best way to do it is HTML and CSS. It has the richest ecosystem, and it is one of the most mature technologies in existence. JS / TS are the native languages for those tools. Everything is informed by this.

Of course, there are other options. You could jam HTML and CSS into (as you mention) Rust, or C, or whatever. But then the ecosystem is extremely lacking, and you're reinventing the wheel. You could use something simpler, like QML or handrolled. But then you lose the aforementioned breadth of features and compatibilities with all the browser code ever written.

TypeScript is genuinely, for my money, the best option. The big problem is that the terminal backends aren't mature (as you said, scrollback, etc). But, given time and money, that'll get sorted out. It's much easier to fix the terminal stuff than to rewrite all of the browser.