From the application-developer side, I'd dispute this. I was told to use Docker + Kubernetes for a relatively small work project recently, and I was able to go from "very little knowledge of either piece of tech" to "I can design, build, and deploy my app without assistance" in about 1 week of actual study time, spread out over the course of the project. And although I have several years' experience, I'm not some super-developer or anything.
What surprised me most is how well-documented (for the most part) everything is. The Kubernetes and Docker sites have a ton of great information, and the CLIs are rich and provide a consistent interface for all the details about your environment. (To tell the truth, that alone makes the time investment worth it.)
After this, there's no way in hell I'm going back to Heroku or similar and trying to piece together their crappy, one-quarter-documented "buildpack" system. I'd take a Kubernetes-and-Docker-first PaaS at a reasonable markup any day of the week.