I think Monzo also received too few samples and should not have been considered eligible: note that the “handling complaints” category didn’t receive any stars, presumably because the 40 people who responded had no complaints.
But “handling complaints” is how you truly know the difference between good and bad customer support.
And why didn’t “value for money” get a star rating? That would only make sense for a bank that had no fees, but Monzo has some. None of the 40 people had used the overdraft?
I think it’s too soon for any fintech to be getting meaningful ratings in a sampling process of the kind Which? does.