I doubt everyone would use the heart rate monitor etc., so I would not judge a device on that. Pixel 2 camera is more than adequate so much so that I am getting rid of my dslr since it is a pain to use each time and lug around. I never have it when I need it and for kids it is not practical to lug around.
Yes the s9 hw may be better but execution and software is a major thing. Search for Max lee and his comparison of the s9 and s9 with pixel camera software etc. and see. I would say if you have to hack and want to hack, then get an s9 and hack it. Otherwise stick to the Pixel. I would not use super slow mo often if ever, that said the P20 camera looks to be better than the S9 as well so it pretty much comes down to what you are chasing.
Great HW and mediocre software - P20
Great HW and good software but mostly gimicky software? - S9
Good ++ (almost great HW) and Great Software - Pixel 2 (everyday use)
I would probably use the zoom on the P20 over the slow mo on the s9. Although I would probably not use either much.
My choice is Pixel 2 xl.