I have mine since 2 weeks, and this is about the same I see. I had a Note 10.1 2014 before, so that's what I'm comparing the Surface to. If I use it the same way as the Note the battery life is about 8h, which is great (consists of browsing, reading, writing stuff, taking notes, watching videos). But then you can use the surface as a full computer, having 5 things open at the same time, recording audio and adding effects to it, gaming, having external stuff attached etcetc. And then battery life obviously takes a hit, which is to be expected.I generally get 6-7.5 hours of light use. I can push it up to maybe 8-8.5 if I turn battery saver mode on. This is assuming that the device is working normally, such as now after the latest updates. If Microsoft breaks something in an update, such as CPU clockspeed, I've gone down as low as 4-5 hours of battery life... or zero if it automatically wakes up in my bag and stays on.
Anyway I feel like I'm getting what I paid for.