I completely agree that all the challenger banks should focus on getting customers from high street banks. But this still means the challenger banks are in direct competition with each other in getting these customers (like I said in my previous post).
For example, if a current high-street-bank-only customer is considering switching to a challenger bank. They are more likely to switch to the challenger bank with the best features/functionality, so the challenger banks are in direct competition with each other for these potential customers who are switching from high street banks.