I wouldn't say the display of the s8 is only marginally better than the pixel. Samsungs displays really are special, and coupled with HDR capability it really is hard to beat, for now. And as much as i loved my pixel XL when i had mine, I do agree that now it is overpriced. Maybe not back when it was released, but for sure now it is now. Considering it does not have water resistance, last gen chipset, i believe it's not worth the same price as a s8+ currently is. Now if you can score a deal on it, then yes, it's still a great phone. But to drop close to $1000 for a pixel XL 128gb now? Tough sell.
I know people value different things, and the things the pixel caters to might be more valuable than water resistance or near bezel-less design. In that case you'll be better served waiting it out as bhatech says, and get the pixel XL 2, than a brand new pixel XL at full price.