Haxe is much older than TS/Flow: it was created in 2006. It's "unsurprising" by design, but there are advanced topics, like pattern matching or macros (AST metaprogramming), and the fact that you're not limited to targeting JS.

It's not as cool (and backed by big Californian co) as JS/TS, but Haxe really grows on you when you start mastering it.