IMHO I think it is reasonable that campaign fares such as SEK 500:- to Paris has low earnings. The big
here is the W.
Especially for SK long haul it is very expensive now to travel in M with 100% earnings. Compare to e.g. Lufthansa. If you book a normal leisure priced long haul flight with LH it will always be in 100% earning booking class. They use the low earnings (25%) classes for ultra cheap or campaigns which is fine by me actually.
Without any specific hard facts, but gut feeling, I´d say a typical M cabin ARN-ORD is filled up to 90% with 25%-earning pax these days. This is a problem for Eurobonus as a program.