At that point you're stuck proving intent. Apple probably knows that their bloat-filled updates slows down old phones and they're probably thrilled that it annoys their customers enough that many will upgrade, but good luck proving that is the reason they're doing it.
well and where is the line between true intent vs lack of caring. if bloat is a side effect of feature creep and project handoffs, slowing old devices is an "unintended" feature.