It takes Apple Watch like 4 apps and at least 1 paid apps or subscription to do what Fitbit does in 1 app with 1 optional subscription. Apple Watch info is split between the Health app, Fitness app, Apple Watch App, and any third party apps you use (which Apple Watch is reliant on to cover uses that Apple doesn’t natively cover like auto sleep tracking).
Also, Fitbit has the best sleep tracking out of all fitness trackers in the market. Apple Watch requires either a paid app for mediocre sleep tracking (via the Auto Sleep app) or you must sleep within your scheduled sleep hours with Sleep focus enabled for sleep tracking to work.
Also, requires daily charging on the Apple Watch while Fitbit lasts 7+ days depending on your model.
Nobody here actually answered your question. Does your health app show Time in Bed or Time Asleep? Those are 2 different things calculated 2 different ways. Time in bed uses your phone to guesstimate your time spent in bed. It is a stupid feature and it’s ideal to turn it off. Turning it off doesn’t actually stop showing time in bed, but it does make it equal to time asleep. Time asleep is a metric that only your watch can calculate