Though even with memory it's not as clear as you assume in the context (which is about browser-based apps). Singular C/Zig/Rust program will surely be more economical than a singular in-browser app due to browser itself having a huge footprint. But what if said user has that browser open all the time anyway as probably most users do? What if there are more than one GUI-rich app, and with browser they share most of the overhead? PLs which allow low-level optimizations offer great opportunities, no arguing. But never say "never" until you know what exact problem yiu have to deal with.

Even though the word performance was used by a parent comment, I think they used it as an umbrella term. The article and most of the talk around rust discord is primarily about the memory. And JVM is probably the worst runtime you could pick if you care about memory usage.