Rent and ownership solve different problems. A fair comparison includes more than rent against a mortgage payment.
Four numbers to include
Treat the deposit as capital tied up in the home, not as money that vanished. Add purchase and sale costs, management fees, rates, repairs, insurance and possible irregular building costs. Then test how long you expect to stay and whether the household can still cope if income or rates change.
Stamp-duty and mortgage rules can change, so verify them through the IRD and HKMA. Use the Rent vs Buy Calculator for a consistent scenario and the Mortgage Calculator to test payment resilience.