While I do agree with you that the 5T is an awesome package and a sweet deal (truly a "flagship killer"), the Pixel 2 line is a bit more expensive also because of things like water and dust resistance; the squeeze to launch Google Assistant; the camera as you've said; and then you have first access to software updates. It also has things that give it a bit of an edge, like the ability to use either AOD or LED notifications. And the 2 XL does have that hefty 3520 mAh battery. GSM Arena gives it an 88 hour rating; whereas the 5T is at 82 hours (still really good!).
You do get a lot for that $300+ difference. Whether or not it is a justifiable price difference is certainly up to the person deciding whether or not to buy the phone. Three hundred dollars is certainly a lot, so it's more than understandable if some people would skip it. I'm personally getting the smaller Pixel 2, and one of the reasons is because I'd be saving some cash by doing so.
Don't get me wrong - I was about to grab a OnePlus 5T a few weeks ago. It's a great phone and I know I would've been happy with it. It's just that there are definitely some things that will set the Pixel 2 line (and specifically, the Pixel 2 XL) apart from the OnePlus 5T. And of course, the 5T has things that the Pixel 2 XL doesn't; such as the alert slider (super cool), double tap to unlock, and other cool stuff. It's all about what features are must-haves for the individual user.