What will most likely be the purpose of the Type 075's air wing ? Anti-sub or airborne operations ?
As type 075's class designation indicate, it is a LHD (Landing ship Helicopter Dock), the primary role of it's air wind is to transport personnel and materials to shore. Two primary air wings would be (1) Z8 and Z20 transport helicopters and (2) Z10 attack helicopters.
Therefore the answer is simple, the main purpose is to use its air wing to send soldiers and light equipment to shore to support an amphibious assault operation, and to provide low level air support to the troops on shore.
Anti-sub helicopters may be stationed onboard, but their primary role is defence against submarine attack rather than hunting enemy submarine. To hunt a submarines your ship must have speed to chase after them, sub hunting may take hours or days, if you haven't sink the sub after 24 hours and you do not have the speed to chase after them, they will have escape beyond your helicopters' range.
So for a low speed LHD, their anti-sub helicopters are mainly for self defence, certainly not primary role of the main air wing.