Are you saying JavaScriptCore is faster than V8?
No. Are you saying it isn't? Please cite your source if so.
Bundling a compiler/transpiler and directing inotify at a source directory (for glorious hot-reloading) doesn't a language "runtime" make. Otherwise, I can create "runtimes" for any language in three lines of code right now.
My bad, they're x86/ARM64 runtimes.