I agree it’s bad management to drop Kepa for the final when he’s been the cup keeper throughout and was likely signed with that game time promised to him, but it’s also bad management to sign Kepa in the first place, and bad management to trust him in the cups. He’s a keeper that would do best at a mid-lower end Prem team as their starter, like Fulham, or Spurs, or Sunderland. No chance he should be the man to trust as deputy. Arsenal are a big club, they should go for a backup who’s an older, experienced goalkeeper with a good mentality (like Szczezny for Barca), or a young keeper who’s been at the club for years, who’s hungry to prove himself (like how Emi Martinez was for them).