With the facts you've presented, I'd move to UA now.

Why?

1. For now, and throughout end of year, you should be able to use the lounge (international itineraries) and maybe get free bags (YMMV on this one) by showing your US membership, even if crediting miles to UA. Then again, you seem to fly enough that you're probably a carry-on only person domestically.

2. 1K is better than Chairman. Yes, folks are going to cite all these annoying losses, but facts only - 1K's better. 1K get 2 domestic UGs and 6 international. You already get 2 domestics as a Platinum, so four total.

The only issue:

As you build up to 1K, you'll get no bonus RDMs to 25K. Then 25% to 50K. Then 50% to 75K, and 75% until 100K. Losing a lot of miles versus US there.