Absolutely agree - happened on MBP, 2 generations of iPads, and Watch...For iPads and Watch, I thought that it might just be the famous battery health vs performance tradeoff they enforce on us, but I rarely ever used the MBP on battery, it was plugged in 95% of the time.
This may be true (not perceptible w/ my apple silicon Macs), but the important thing is that they get slower more slowly than my wintel gets slower (I blame disgruntled Windows and/or nvidia drivers devs....)