At the end of the day with or without a 40 cent discount, flying Vancouver to London for $322 is a pretty cheap deal. Still as to fees there is nothing shown for the security fee, AIF, NAVCan just fuel surcharge? (the latter which is ostensibly what they pass YQ off as). But to be sensible assume most fees are legit, and they pay them, they are not giving 20% off something they pay 100% of to someone else. I think within the ATC are more things than YQ. You don't even have a penny of GST for example or Vancouver's airport improvement fees. The e-ticket shows a full breakdown. The quote you show says other ATC not YQ.

I booked a fare today with my standing 15% discount off all base fares that I have and it was 15% off the fare with the charges and taxes added to that after. There were fees, of which YQ was 40% of the total give or take.