I don't consider the design of TypeScript a weakness at all. TypeScript is really well designed and is great at what it does. The type system they came up with

I don't consider the design of TypeScript a weakness at all. TypeScript is really well designed and is great at what it does. The type system they came up with is pretty optimal for modeling real-world JavaScript code. But the tuning they did around the JavaScript ecosystem means it's not a great language to use for generating efficient native code. I started ThinScript in part for exactly that reason. I want good tooling and rapid prototyping, just for native development instead of web development. That requires a different set of trade-offs and design decisions.