I found Scala to be an extremely enlightening language: it taught me a lot about functional programming. But, the complex type system and the sacrifices needed to ensure Java compatibility entail many quirks that I find frustrating. I think it's actually a similar dynamic to what you mention: "retro-fitting these features onto an existing language never fits quite as nicely as a language that was designed with them from scratch."
BTW, I am a huge fan of your writing: the Principle of Least Power is a sacred programming text to me .