I would expect that a fist rate airline like CX would have fewer aircraft substitutions.

part of the problem is they are inconsistent.

if you look at BKK-HKG flights, some days have F (sold as F) on the 747 and some days are all 330.

some days are a mix of 777 747 and 330 .

with 5 or 6 flights a day with a diff aircraft type each day of the week, things will go wrong and last minute substitutions (downgrades)will happen.

Until CX starts using the same aircraft for specific flights, you can expect this to continue