He didn't say inertia, he said mature. It take a while for a language/platform to develop a solid ecosystem and stabilize. That absolutely has value, and is something you can't get out of a new system no matter what novel problems it solves.

As far as new apps go, yeah I think it's still pretty optimal for a huge swath of web apps, especially for early incubation when you have <20 engineers and you need to move quick. Not if you need web sockets, or other concurrency / performance critical applications though.