It's definitely a mental issue within the squad. In the past four years, three of those years have seen Lancs find a way to snatch defeat from the jaws of victory in a T20 knockout match. David's innings in the final was truly bizarre, came in prodded and poked around for a few overs (which isn't the way he plays at all and then got out. Why not just play your natural game and hit it out the park from ball one. The Ashes is in June/July next year apparently so the Aussie white ball players should be free. Sack him off and bring back Maxwell.
The pressure of a big final, you can't replicate it. Nathan Ellis though put it probably the finest death bowling performance I've seen in a long long time. He'll surely be lining up for Australia at the T20 World Cup. Plus James Vince is an outstanding captain, the best in the country by a mile.