I did not write the blog post, it was just a simple
infer/
extends non-trivial example explained in depth, commonly used in packages like
express and so forth.
TDungeon [1], a game running on the TypeScript type system, really showcases how powerful the type system truly is.
Why not C#? Probably because Anders Hejlsberg [2], lead architect of C# and core developer of TypeScript, wanted something different. More of a sociological, rather than technological, reason.
[1] https://github.com/cassiozen/TDungeon
[2] https://en.wikipedia.org/wiki/Anders_Hejlsberg