Under his review it sounds like it was downgraded for prevention of cooling issues.Well, according to this review, after a 20 minutes graphic intensive testing, the A19 Pro on the iPhone Air is worse than the A19, and that's after a couple of tests, one of them inside a fridge to keep the Air as cool as possible:
Sounds to me like the A19 Pro version used in the Air is powered down to assist with battery life or something?. Definitely gimmicky.