It does seem that degradation of batteries is slower initially as reported by Apple’s battery health measure. My Apple battery dropped very quickly from 100% to 98%, but the battery health for my other Apple devices often stay at 100% for a long time.
Interestingly, Figure 17 of this article shows that battery degradation occurs faster at the beginning.
That’s interesting, I wonder if Apple either Pre-stages the batteries to cover the Acceleration stage, or factors it in with software so that 100% is when the acceleration stage finishes.
They treat the acceleration stage as " burn in’, and then battery monitoring starts at beginning of the stabilization stage. The battery then degrades linearly for at at least as long as the two-year warranty period. At which point, the saturation stage kicks in, and fairly soon the user will want to upgrade the device or replace the battery. Of course, I’m putting a lot of trust in this one idealized graph, but this pattern does fit my experience.