Marketing a specific "hours of" battery life for a watch is always total non-sense.
Features like playing music, blood oxygen measurement, HR accuracy (sampling interval), GPS accuracy, LTE, screen brightness, phone calls, screen mode (always on, wrist based), connection to wifi, connection to phone, LTE/Wifi signal strength, apps used, watch face, ... etc will all affect the battery life immensely. Depending on settings the same watch can have anywhere between 10 hours to 10 days battery life.
Would be great if Apple would have a battery-life estimator on their page. Allow one to tune parameters. That would educate the buyer on features and demonstrate that competition might be telling a more misleading story on battery life ...
I would not be surprised if Apple Watch Ultra will get 10+ days of battery-life if one turns everything off. Apple just would not want to market that as it would set wrong expectations.