I hate to say it, but MR is a massive energy hog. Adblockers will help on this site. Bestbuy and Apple are pretty clean. I know this because I've done tons of testing as to which sites drain battery and use resources. You can really only do this with Coconut Battery to see what your power usage is for all of your different applications. After you are armed with a little knowledge, it's easy to achieve claimed battery life. You need to average 8 watts on the 15" to get 10 hours more or less. You can see if you are using Coconut Battery. If you want to continue to work normally, you'll just understand what the tradeoff is.
The issue is these "energy efficient" skylakes (and dGPU in your case). The software powers them up and slows them down as needed to maximize battery. As long as you understand when they are doing this, you'll understand what to expect from your battery. People can keep repeating that the battery is smaller, which it is, but that doesn't explain or solve anything. The smaller battery is matched with the more efficient chips. People need to reset their calculations since this is a significant change from past generations in terms of power usage.
As someone else said, browsing is wildly inconsistent based on different sites in terms of power usage. I recommend an adblocker, but some sites will still drain more than others. It is up to you if you want to go through this to inform yourself. You are certainly entitled to return the computer as it is not getting 10 hours out of the box (with light use). I like mine, so I put in the time to understand it.