Hotel brands set their minimum standards for elite benefits and Hilton sets a low minimum standard, compared to Hyatt or Marriott, but individual hotels can go above and beyond those minimum standards (and many in China and elsewhere in Asia often do). In the US, there're simply too many guests with elite statuses (particularly Hilton, because Hilton Gold, for example, comes automatically with a $150/yr AmEx card).

Generally speaking, you wouldn't get elite benefits (upgrades, free breakfast, etc.) when you book through a third-party OTA (some premium credit cards offer their own specially curated hotel collections that provide similar benefits if you book hotels in those collections through such channels). Again, some (few) individual hotels may provide some elite benefits to their frequent guests even though they aren't required to do so.

I generally don't book stays at hotels where I have elite statuses. Because hotels in Asia (including China) tend to provide better elite benefits (and more of them provide executive lounges), booking through an OTA (including trip.com) almost never makes sense if you value those elite benefits (or stay credits or hotel points), IMO.