Then you had the special AirPod Pro 2s.
This is what Apple says you should have expected from them:
AirPods Pro
- Up to 6 hours of listening time with a single charge (up to 5.5 hours with Spatial Audio and Head Tracking enabled)4
- Up to 4.5 hours of talk time with a single charge5
AirPods Pro with MagSafe Charging Case
- Up to 30 hours of listening time6
- Up to 24 hours of talk time7
5 minutes in the case provides around 1 hour of listening time8 or around 1 hour of talk time
AirPods Pro 2 - Tech Specs - Apple Support
Here are Apple's specs for the AirPod Pro 3:
AirPods Pro 3
- Up to 8 hours of listening time on a single charge with Active Noise Cancellation enabled (up to 7.5 hours with Spatial Audio and Head Tracking enabled)
- Up to 6.5 hours of listening time on a single charge with heart rate sensing during workouts
- Up to 10 hours of listening time on a single charge in Transparency using the Hearing Aid feature
AirPods Pro 3 with MagSafe Charging Case (USB‑C)
- Up to 24 hours of listening time with Active Noise Cancellation enabled
- 5 minutes in the case provides around 1 hour of listening time22
AirPods Pro 3 - Technical Specifications - Apple
Mind you, I don't see what that has to do with your original statement. You make an observation about the fact that if your AirPods charged up from the case, the charge on the case dropped. You said nothing about time.