I have the same issue, i called support and have talked to their senior tech. The steps taken - reset watch thrice (2 as new and 1 from backup), noted the depletion times, apple support ran diagnostics and also took screenshare of the phone to check setting. Also sent photos from the apple watch screen. Batter life at 98% on apple watch 6. The battery lasts for 7 hours and then asks to charge again while it easily lasted for at least 1.5 days.
Apple support is defensive and rude. Also the genius bar personnel is trying to avoid any visits. The support staff always is trying to say always that you will have to pay for any issues even though its in warranty.
Going through the posts definitely looks like software issue. Almost same issue is also happening to my wife's apple watch 6 and her battery percentage is at 100% but she does not use it as much.
Apple are you listening. You need to work on your support staff on Apple watch, completely different experience from other product lines. Fix it, you may loose customers due to service issues.