Personally, I think the fares WestJet have came to market with are competitive (and as per my earlier post are comparable with GLA and EDI, the only other regional departure points in the UK). As FLY puts above, you’ve got to consider a lot more than purely the flight cost when looking at this, and factor it all in - Quoting figures purely from flight only is the incorrect way of doing it.
I’ve also seen comparisons being made to LHR flights without baggage, to CWL flights with baggage, which is also (and definitely more) incorrect.
I’ve looked at other WestJet flights and those 15 or so seats always appear blocked on the seatmap, so I have no idea where they’ve got those figures from. They must have got it from somewhere as they aren’t exactly going to take them out of nowhere and quote random numbers !