Like rewards, the Monzo app and user experience has a value too. Also, a really terrible UX has negative value in the same calculations. My personal highest payout rewards Mastercard is my Aqua card at 0.5%. But, if I value Monzo’s great experience at, say, 0.2%, and I put Aqua’s terrible experience at -0.5% (it’s so bad, it’s equivalent to nothing to me), Monzo wins by a mile.
My Barclaycard freedom rewards Visa has rewards worth about 0.3%. But I’ll value lack of Android Pay at -0.3%. So again, worth nothing, and Monzo wins.
Avios have so few redemptions that are really worth bothering with (short-haul flights in Asia? Some of the non-flight redemptions, but at a very low value) that I’ve never been bothered to even consider that route, either (the Tesco credit card works out, what, something like 1/3 of an Avios per pound spend? That’s nothing for my needs).
Amex has the only rewards that can outweigh Monzo to me, but the negative value of the hassle of using Amex (which I’ll consider a fixed negative, not a percent, as it’s far more worth it on large purchases) makes them pretty similar to me.