This post is more or less all about them extending things they already do for lower resolutions to 4K. And the graph you posted isn't quite showing what you're

This post is more or less all about them extending things they already do for lower resolutions to 4K. And the graph you posted isn't quite showing what you're saying it is: these show the "4K" curves. When you're on a 1080-max device but have a strong connection, there are higher-bitrate 1080 streams available; they're just not on this chart because that's not what it's showing. In other words, what the curves are showing is just that they're switching to higher resolutions at lower bitrates than before, when your device supports them. Really the way to read it would be drawing lines vertically: given a fixed bandwidth, the "optimized" encode is always giving higher quality and often higher resolution.