Perhaps. Given the nature of the brain spectrum, it makes sense to use a window with greater roll-off than the slope of the brain background/aperiodic component, at least when using FOOOF since we're interested in that component. However, the problem may not be as bad as this simulation data makes it look. Luc mentioned he did not observe the windowing effect with real data. I guess it depends on the relative amplitude of peaks vs the background. Still, is there any reason we would want to keep Hamming as the default other than compatibility?
At the very least, I think we need the option of choosing the window function.