The Asia argument is somewhat problematic. Sure, Hiltons in Asia take care of Diamonds. However, basically all chains do take good care of higher-tier elites.

So I don't take issue with your claim per se. It's true Hilton Diamond is not worthless in Asia. But it's not really an argument to concentrate on Hilton. I might just as well book according to price (or promos if my employer is footing the bill) and see with what elite statuses I end up with. As long as I stay frequently enough to make a decent status level in 2-3 programmes, I'm gonna get treated well. Doesn't necessarily have to be the very highest tier, I've had excellent experiences in Asia as Accor Platinum (not Accor Diamond) or at Intercontis as Spire Ambassador (not Royal Ambassador).