Sure. You get 21 hours, as long as you don't use the cell radio to make calls, or get data. It works decent over wifi, but even then, 3 hours, of screen time, is actually not very good. It's great for us Galaxy users, but that's because we don't know any better.
Make some calls, use that cell radio, watch that battery life drain in front of your eyes.
Hell, even your graph shows long periods of non use, and when you did wake it up to use it, the battery drain was steep and fast, so you put it back in sleep and didn't use it for a few more hours.
That said, you used almost zero mobile netowrk signal, which murders that battery. Any device can get a good battery graph with wifi.