I think there's a pretty good case for the arrow being easier to reason about especially with anonymous functions or if currying gets involved. The other way is lacking a "verb" and it becomes harder to keep track of what's going on in some cases.

The arrow is also conventional in ML family languages, which are a venerable branch of programming whose traditions I respect and enjoy. That's not enough reason alone to keep it maybe but it's not nothing either.

The colon thing whatever, I truly just can't bring myself to care about such fine-grained specifics of syntax. It sounds like a rough life honestly.