There was nothing "complex" about the Whirlwind (or any other high performance twin) that adequate training couldn't take care of, just two of everything.
Part of the problem with the Whirlwind was that it was late. Its' designer Petter over-promised in order to win the contract and under delivered in execution and time. Westland was at the time of the order in 1937 a middle size manufacturer of staid biplanes of very conventional construction, and the Lysander, which wasn't much different structure-wise, and its overly ambitious and prickly designer conceived the Whirlwind, which for its time was a thoroughly modern design incorporating what Petter believed were advanced features. Westland's workforce needed to learn new skills in mass producing all-metal stressed skin aircraft, which the company had not production-line manufactured before, so the thing was late and deliveries were slow since it took the company time to build it. That was even before it didn't live up to expectations.