We never signed the Hague Accords and are not bound by them. The US military prefers FMJ designs over HP partly because they feed more reliably, but mainly because they penetrate barriers and light armor much better.
The effectiveness a HP would have over FMJ would be minimal especially in rifle rounds. It is a trade off, but the military considers increased penetration through barriers more important. For military use I agree.
Civilian use is different. Shooting through a barrier is less of a concern. Putting someone down quicker with less need for multiple shots and not having a bullet overpenetrate is a major concern for civilian and LE use. HP bullets are the prefered bullet for this use.
I don't think of our calibers coming full circle. It is more like womens fashion. Styles come and go, then come back again.