Just for comparison, I thought I'd look at other numbers for flights operating UK-Doha in March.
So Cardiff's load factor was 55% in March.
Birmingham had 11,485 passengers meaning a load factor of 73%. That's a pretty big disparity considering the numbers were very close last July and August. Is Cardiff rally that much more seasonal?
Edinburgh had 11,523 passengers giving a load factor of 66%.
Manchester had 25,893 passengers. I'm not 100% on the schedule, but I presume there were 62 A350-900 and 18 787-8 flights in March.That gives a load factor of 59%. Not a great LF - However, I'm not sure if QR operated all of those flights.
London Gatwick had 24,039 passengers. That gives a LF of 77%. Perhaps not unsurprising as Gatwick is always cheaper than LHR.
Heathrow had 89,779 passengers. I'm not able to work out LF accurately as the flights are too variable. If you took this week's schedule to be the same as the one in March (2xA359, 1xA380, 1x77W and 1xA351 daily), it would give a LF of 77% just like LGW.
Of course, none of these figure mention yield.