AK1 It would be interesting to know in what ways were the meals a disaster and what exactly was/is the expectation ?
Special meals are by definition not 'normal' meals in the broad sense and they obviously cannot offer the broad variety and choices that a 'normal' menu offers catering as they do for avery small minority of passengers .
'A total meal failure' sounds perhaps a little OTT. I have often seen the ex HK and UK meals and definitely there is no dairy in ether.
Perhaps in the above case the fault was that the wrong meals were delivered to the flight or wrongly ordered by the pax.
Who at Cathay did you call re the meal request,was it MPC? Did you have the CC make a report ?
A couple of vegetarians that I know sometimes BYO
At some major airports outlets offer 'take on board' vegetarian and I believe Vegan meals and these may offer a good option to the no-choice on board offerings. Better hotels in Asia I know are happy to pack take on board meals if requested and I am sure that goes also ex other major cities

Cathay special meals lists the following.
Vegetarian Vegan Meal Strict vegetarian food with high protein, rich iron and high calcium.(VGML)Vegetarian Raw MealCombination of raw fruits and vegetables along with pure fresh fruit / vegetable juices.
I have vegan business associate who has no problem at all with the 2 above meals (definitely 'no dairy)' ex HK but some outstations offerings she says are problematic particularly ex USA.