The design issue is that people wanted-or Apple thought they wanted- really thin phones. Thinner phones means smaller, less capacity batteries. From others on this thread evidently it also means lower quality, but I haven’t heard that before and I am not knowledgeable about different battery manufacturers so I can’t comment on that. But I do think a lot of design decisions were made based upon looks rather than practicality.Apple is getting away with something here if it ends with this. There is a reason they are quickly offering everyone a $29 battery replacement (for a year only) to get this to go away. Total speculation by me, but I believe there is a design issue here that is causing their devices, starting with the 6, to become unstable when the battery ages. I've never heard of a device needing to be slowed down when the battery ages. They are probably doing this to avoid a mass recall. Hopefully the court cases will do enough discovery to really find out what is going on. Apple is probably quickly fixing things in the newer devices so this isn't a problem, or isn't exposed. And by then, most of the older ones will start to reach end of life and this will blow over.
But I don’t think Apple was intentionally trying to cripple phones to force customers to buy new phones. In a company where people join and leave every month, policy descisions like this are hard to to keep secret since a fair number of mid level people would either be in on the secrete or know enough background to figure it out. And someone would talk, at least anonymously. Over a period of months, you can keep a secret among more than 3 people truly secret provided all but 1 of them are dead.