Air Passenger Duty from the UK to HK is currently GBP 150 for business class/premium economy and GBP 75 for coach. This is probably whyyou paid so much. it's the British tax man ripping you off, not CX.
we have about 6 people at the gate counter to load an a330 and delta can do it and handle staff with maybe 2-3 people
United need a few more than that in case of offloads!