While the idea behind the slow downs is solid and I’ve done it myself on old laptops with bad batteries, doing it behind the scenes without informing anyone and then making money by selling new devices

I genuinely believe this was a case of bad comms rather than ill-intent. I say that based on time spent within the company where there was an insane (in a good way) focus on the customer experience.

Apple will fuck around with shit like the App Store and dick-prices for RAM but they won't risk their image by doing stupid shit slowing down devices to encourage new purchases. New software features are the carrot to encourage upgrades / new purchases. There is no stick. I can't tell you how much shit got punted to fix things a different time when people cried foul because devices got slow.