DeHavilland built beautiful airliners pre-war. To my knowledge, only the Flamingo was all-metal. They certainly had no experience in pressurized metal structures. Boeing had its Stratoliner, B-29 and Stratocruisers, Lockheed itsL949 Aand Later Connirs and Douglas the DC-6.
De Havilland had to cope with metal, pressurization and very high altitudes (compared with pistons) so the learning curve for them was much steeper. Perhaps it is not so surprising they stumbled in the structural area.
They were gutsy to leap ahead of everyone..A beautiful machine with deep flaws.