Samsung is set to unveil the Galaxy S10 phones next month. The biggest of the three, the S10+ will apparently be only 7.8mm thick, which would make it the slimmest phone ever with a 4000 mAh battery. In comparison, the S9+ with a 3500 mAh battery was 8.5mm thick.
https://www.notebookcheck.net/The-Samsung-Galaxy-S10-will-be-slimmer-than-the-S9-while-also-featuring-a-bigger-battery.394091.0.html
Thinness and battery don't matter if the phone isn't usable and/or isn't "mine." The first questions for every new phone are, "is it rootable?" and "does it have a headphone jack?" If the answer to either is "no," then we don't have a good phone. Apple and Samsung and Google can blame poor sales on "saturation" or whatever they can think of to cover up that people don't want their crippled phones, but it's no coincidence that as they strip the headphone jacks and ability to customize the sales plummet.