They should have brought you in as a consultant so that they would have arrived at the correct decision. Alas, they are now doomed to be wrong forever.
They had a custom language giving them full flexibility to achieve making a product in the browser that put them ahead of everyone else, and instead of embracing that, they throw it out to be able to hire of the shelve developers to code in a language that doesn't let them move freely. Typescript is like crutches in the sense that it might support you in not falling, but you only really need them if you're crippled in some way.
What are you talking about? Typescript is a fantastic improvement on JavaScript.
Skew doesn't look fundamentally better enough that it would be worth the downsides. Lack of IDE support alone is probably enough to cancel out a productivity gains from a better language.
I like that typescript catches when I need to do null checks so I don't end up with the most notorious runtime error seared into the brain of every JS developer "cannot read property of undefined".
Some parts are nice, like the string literal typing "this" | "that". Other things are hacky, like "branded types", gross.
But then I think of my commercial codebase which is extremely well tested, regular old JS, and wonder if is worth the hassle.
