If you're a new joiner and trying to decide which fleet to opt for, here are my thoughts:
A350 will take over the "long thin routes" as the A340 used to fly previously (until 4 engines became inefficient). The 777 will continue to do the bulk flying as was previously flown by 744.
Think - A350 most of Europe ex-London, some smaller capacity North America, and opening up some Central America, and new MEA, Aust and Pacific destinations.... POSSIBLY less than daily (so better for crew if you need to rest downroute due 3 crew ops/ or like longer layovers).
777 - think all of the big solid ports... LHR, FRA, CDG, JFK, LAX, SYD, YVR, YYZ... etc. daily, to 4X daily.
A330 will still be flown regionally on the lower capacity routes. And that will include India 2 crew WOCL, MEA, Asia... Some Oz destinations. If you fly A350, you will have to start A330.
CX has decided to move away from being a premium carrier by not ordering A380's. CX moves toward a cheaper, high frequency product, and a more conservative business plan.