I think the split between Monzo and Starling is probably closer than it appears.
Monzo have 1 million active users and I believe a third of them are paying their salary in (or perhaps it’s a 3rd of 1.5 million, it doesn’t matter).
Starling have 500,000 customers, but no stats on salary - I’d guess it’s more than a third.
I still honestly think the big banks will end up with feature sets far closer to the challengers than they currently have, which limits the “marketing” Monzo/Starling can do.
I also don’t see many customers in the UK changing banks due to “ethical or moral” reasons.
When it comes to money, people seem to like familiarity and safety.
I’ve spoken to quite a lot of people about Monzo/Starling, and one of the questions they always ask is “what if they go under?”.
You just wouldn’t get that question if you said “I bank with Barclays”.
It’ll be a long time before those thoughts disappear.