The Galaxy S9 is a fine phone, but it just launched and its price hasn't had time to cool off. The Galaxy S8 is a different story. It's price in the UK is under £500, compared to £740 for the S9.
You can go lower than that by getting a seller-refurbished unit from eBay. A Vodafone unit in Pristine condition is £430, the unlocked one is £470, so not really worth it. Note that this is for the Black model, other colors cost more. Dropping down to Good condition, the lowest price is £360 (Grey phone for EE), which is at least £100 off a new unit.
Gsmarena mostly checks standby time. Check all the forums in the world. 5t wins (by far) in SoT (which is the metric that matters to most)
I can show couple of videos where S9 won all of them :) U told that sony won s9 in performance, do you feel difference between 259000 and 250000 points ? :D :D I dont feel difference between 130000 and 160000 in real life ;)