If Google had a policy of sending people new phones in an RMA that completely changed by the time the Nexus 6P came out. If you use your phone for one day and need to RMA it they will only send you a refurbished phone. The Pixel forums on XDA are dominated by fan boys. You should read the official Google Pixel Support page if you want to get a more accurate sense of what's going on with that phone.
It's definitely possible that Google's RMA policy has changed in the past couple of years. I don't think I've RMA'd one since the Nexus 5.
But in the days of the Nexus 5, if you needed to exchange your phone you paid full price for a new one, they sent you the new one in full new retail packaging with all new accessories, and you sent your old phone back. Once they received your old phone they'd refund your money. In those days they absolutely did send you a brand new device.
Now I'm curious what the current RMA process is for Google's phones.
On another note, I'm in a very similar situation as you. I recently sold my Pixel XL as I've been using a Galaxy S8 as my daily driver. However, in 2 months of usage I'm already tired of Touchwiz and looking at other more "pure Android" experiences. I almost pulled the trigger on the OnePlus 5 but decided to hold off and see what the Essential Phone had to offer. Aside from the bezel-less look, early reviews of that phone aren't too positive due to the LCD screen and the sub-par camera.
So now I'm back to looking at the OnePlus 5. But with the 2nd generation Pixel/Pixel Xl due to be announced in early October, I'm finding myself in a holding pattern for the time being.