It's a matter of experience, these engines aren't simply turbocharged engines, the energy recovery systems force you to forget everything you know, and basically start at zero. You cannot treat these power units in the normal sense, the thinking has to be in how do you extract the maximum from the MGU-H, as in how do you recover the maximum from the exhaust. I've said it before, you may be down 30-40hp but if you gain 160 as a result(ie longer deployment) then it's worth it.
To be honest if I were starting out in this formula, I'd be better served studying this
than any past f1 engine.