Well I guess we didn't read the same articles, I saw just north of 8hrs for the S8. Maybe give it a couple of days.
If it picks up to 8 hours I'll be more than happy. Admittedly I've got AOD active, which will have knocked 7pc off my battery so far, going on reports of it using 1pc per hour. It's such a useful feature that I don't want to turn it off, since it covers up the failings of the fingerprint scanner (most of the time I have to unlock my phone it's only to check the time)