That is hardly a scientific test. First of all, battery life is not linear. The first 10% take longer to drain than the folllowing 90%. This is because iOS does not start draining the battery meter until the device is really at 95%.
100% reported = 95%
50% reported = 47.5%.
So your battery is not at 100% but someone in between 95-100%.
Second, your usage is different. You are connected to WiFi calling instead of cellular network which off the bat uses less battery power.
Third, I'm assuming that screenshot is you sleeping overnight. That means you have 35 minutes of background usage without touching the phone. I guarantee you if you did the same exact thing with the watch connected, the results would be the same. I wake up with 10 minutes of usage and 7.5-8 hours of standby and my phone at 100% as well.
If you truly want to see if it's the Apple Watch (I'm 100% certain it's not), then you are going to have to at least control your variables. So unfortunately that screenshot means absolutely nothing.
OK, so the Apple Watch app was responsible for 6% of usage and was on screen 27 minutes - clearly, you were spending time pursuing this 'Watch is the cause" theory. Twitter, meantime, is responsible for 50% of usage. Why, then, do you think the Watch is the cause?
I suggested you un-pair the Watch. You haven't mentioned trying that. If you haven't done that, why? It's the surest way I know of confirming/eliminating the Watch as a cause. It's sure a whole lot more effective than returning the Watch. What if you returned the Watch and it didn't fix your problem???
If you don't take that simple step, I have to wonder whether you have a different motive. Perhaps you want to return the Watch for other reasons? If you really wanted to keep the Watch, wouldn't you try to eliminate it as a cause for the problem, rather than persist in the unproven belief that it is the cause?
I really wish the battery stats were for the current period since being unplugged, not the last 24 hours. What I did yesterday has no effect on today's battery, so why is it there?
I think it's expected for the Apple Watch when paired with the iPhone to have an effect on the battery life as it's a constant Bluetooth connection and is using mobile/ wifi data.
I first used my Apple Watch with the iPhone 6 Plus and I did notice that my battery life was shorter but not by much. Not more than 10 % over the day. I've always used my Apple Watch with my 6S plus and 7 plus so I wouldn't be able to tell you the difference.