it seem the regulators whether GCAA, CAA, FAA EASA etc... do not really scrutinise or challenge the operators when they apply for variations to this original scheme to make it fit longer flight times,
Regulators (not GCAA) do take action when there are enough complaints. Consider recent FAA investigation and conclusion that UA has system wide issue with its schedule. How did FAA arrive at the conclusion, union complained to FAA about every minor discretionary flight.
AI's Australia route is another well know example where regulator/airline gave in to union complaints. AI had a tag in Australia which required two landings in 11-12 hrs. Over 7-8 months AI operated this tag, union crew lodged 185 complaints. DGCA/AI couldn't take any more and dropped the tag.
And of course AF unions need no introduction.
Guess who uses news like these for their own benefit, EK.