I am a Scala developer but I agree with your points. The only thing that just simply drives me mad in Rust is mandatory semicolons. Once you are used to be able to omit them then it gets really annoying to go back using them.
"For the most part Pub/Sub delivers each message once, and in the order in which it was published. However, once-only and in-order delivery are not guaranteed: it may happen that a message is delivered more than once, and out of order."
(edit: added translation of unit)