The designers got to mostly start from scratch (some things are there for JS compatibility) not only at the language level, but importantly also at the VM level

The designers got to mostly start from scratch (some things are there for JS compatibility) not only at the language level, but importantly also at the VM level. It's already ~ 2X faster than V8 and they believe there is room for more performance gains. Then add in all of the nice language features beyond classes and types and you have something worthwhile.