I was thinking about the same thing the first time I read this. He'll lose substantial low end torque.
However, he's not going to be lugging the engine down like that unless there's an off road excursion. Most of his time is spent in the sweet spot of the power band. I doubt that engine spends much time below 3,500 rpm.
Derek is one of the few folks that may actually benefit from the lightweight flywheel.