The form found lacking in Apostolicae Curae is not invalid in itself. It not exceptional, in that some Rites which the RCC does recognize as conveying sacred orders validly, partake of the same “defect”. That is the point of intertwining the concept of invalid sacramental intent, in the conclusion of Apostolicae Curae. And note that sacramental intent is not the “intent” of a Rite, or of the form of ordination,
The history of this tale; long, sad, and rife with politics, theology, personalities and even more history, has been a hobby of mine for roughly 20 years. My recommended reading on this sad subject is invariably Fr. J. J. Hughes ABSOLUTELY NULL AND UTTERLY VOID, for pure history, and his STEWARDS OF THE LORD for some thought-provoking theology. And ANGLICAN ORDERS AND DEFECT OF INTENTION, by Fr. (as he was at the time) Francis Clark, for the best exposition of what the Apostolic Letter was saying.
And on all of this, Anglicans have their own views. Not that you need to take that into consideration, to be sure.