[ahoge]

>Classes. Whoop-dee-freakin’-doo.

There are dozens of ways to do classes/inheritance. Standardizing this means better tooling, documentation, and interoperability.

>Default parameters. By itself, this is another “so what” feature.

It's extremely useful in conjunction with named parameters. Named parameters are so much better than "option" objects.

If it's right in the function's signature, you can see right away how this thing is supposed to be used. Since it's declarative, it can be also picked up by your editor, too.

>let considered harmful

No, it's not. It makes variable declaration work like everywhere else. Function scope is the super weird anomaly.