I am trying to get a better understanding of CX approach to the light/essential/flex pricing in Y.

The website pricing is based on the lowest available fare bucket for LIGHT. Then they add a (small) surcharge for the benefits of ESSENTIAL ( regular seat selection, 1 more bag and a tiny reduction in the change/cancellation fee, upgrade with AM), but keep the same fare bucket. Then they had a (small) surcharge for FLEX. FLEX has no change fee but still potential fare difference and the same cancellation fee as ESSENTIAL. SO FLEX is not really that flexible.

That is somewhat different from some airlines (e.g. QR, AF) where moving across the fare family implies a change in the fare bucket.

Am I wrong?

PS: in a current booking a pax who booked long ago had a much cheaper FLEX than one who booked later a LIGHT with worse restrictions (bags, fees, etc). Of course, the earlier pax had a much lower fare bucket than the later one (with worse restrictions for the later one). I hope that I am clear but they are both family members and I did the booking.