You guys are missing the Santander's extra 25% on flights.
The mechanics is that the 25% is on the base 5avios/spend, so an extra 1.25/spend.
It's added to the monthly santander avios payment (on the month the flight is flown), so it will count towards the avios earned and will get 10:1 PE.

The formula for Santander is
FareYQ * 0.9 * (0.5 + 1.25) + Tax *0.9 * 0.5
and Icon
(FareYQ + Tax) * 0.9

Let's say annual spend of 4k on FareYQ and 500 on tax, pre discount
Santander earns 6525 and the Icon 4050.
If all you fly is super cheap tickets with tiny fare and relative-then high tax then the icon comes out ahead, but then stick with segment running.

When combined with 3eur/month no foreign currency fee, so 7/month, so slightly cheaper than the Icon, but earns 2:1 on everything, as well as the twice annual 50% avios promo, the Santander (even the basic premier one) smokes the icon.