This is as much as a myth as form is irrelevant in cup finals. We were in poor form and played exactly the same when we lost to Man U in last final, and we were in poor form and played exactly the same when we lost to Sunderland this season
The quality of every side in the league has improved by a huge margin over the past 5 seasons. Honestly don't understand this point at all, every team can beat any other team on their day.