Rust is a great language but that's a pretty insane statement. The ecosystem is still tiny compared to the JVM.
However, I must say that Rust is also a very productive and quite powerful language (albeit IMHO not as powerful as Scala) and Scala is actually not that bad at performance either - probably better than a vast majority of other languages out there (albeit not as powerful as Rust or C++).
As far as ecosystems are considered - this is really hard to say. Rust has the whole C (and most of C++) ecosystem at hand plus a few really amazing Rust solutions like Cargo. Scala is limited mostly to JVM and JS, which are great ecosystems, but it is not true they offer everything. And there are still some caveats when using Java tools with Scala (e.g. profilers, debuggers or build systems).
And I have no problem with the JVM interop. As long as you don't try to write Scala libraries that need to be consumed by Java applications, everything just works really.
No, it's not. You can call native (C) functions from the JVM.
That said; nowadays you have the Native and JS runtimes as possible targets as well. Scala.js works surprisingly good with very few caveats.
Kotlin doesn't bring anything new and is full of ad-hoc design decisions, and Java itself is catching up (and even potentially surpassing it, see pattern matching for instance). I don't think it's a huge threat. Sure you'll see people who didn't really understand the point of Scala move to Kotlin because they just wanted a better Java really, and Kotlin does that well. But I think it's been clear that Scala shouldn't try to pursue this goal, for the past 5 years at least, after the hype around Spark cooled off.
I'm happy that Scala 3 is focusing on the biggest pain points. I'm also quite happy with the resources that have been added behind the tooling and ecosystem lately. The Scala center wouldn't exist if there wasn't a real demand for improvements in the mid to long-term future.
