Apple's mistake was really that they didnt do proper load testing on their batteries. Had they shipped a battery that was capable of keeping up with the phone, this wouldn't have been a problem to begin with.
Instead, they pushed their users to buy new phones, or pricey fixes for a manufacturing mistake
Because we saw the evidence: The batteries they shipped started dying early. I'm willing to believe that they did do proper testing and ignored the results, but I'm not sure that's better.
I'm not a battery engineer, nor a battery tester, so I cannot comment on what a proper test would be, and if that would include testing the battery for extended period of time prior to releasing them to market.
But you don't need to be a battery engineer to understand statistics. If these batteries are dying early, then either Apple didn't do enough testing, they did and ignored the results.
Instead, they pushed their users to buy new phones, or pricey fixes for a manufacturing mistake