You have a hard time believing that their team experienced more happiness and productivity with TS...because your ReasonML code compiles a lot faster than your TS code?
They become really frustrating as the project grows in size. Personally, it becomes really difficult to maintain productivity. As compile times tick up, I start bouncing over to other tabs rather than just twiddling my thumbs starring at a terminal. Then I realize I've been on Reddit for a half-hour.
I recently watched this talk by Johnathan Blow[0] where he talks about quality of life in programming languages and spends a fair amount of time talking about compile times and their effects.
I think we collectively need to re-align on being performance focused. Tools are simultaneously amazing but crummy at the same time.
I don't love the compile times, but I'll also say with TypeScript I tend to check the browser that often. TS also means simpler refactoring, for example.
Note also:
* type checks can run in parallel, so they won't block your other build block
* the tsc has been making gradual improvements to performance and techniques to improve compilation and type checking
* there are speedy alternatives to the TypeScript compiler (tsc) (eg: https://sucrase.io) for transpilation
I had actually been watching Deno in case they solved any of that.