One important factor with regard to a windmilling prop is the powertrain configuration, the PW100 series are free turbines so a windmilling prop will, in effect, only be driving the power turbine, hence the general lack of NTS systems on these powerplants.
Compared to a Garrett (for example) where the prop will have the job of driving the turbine and compressor assembly and the windmilling drag will be very significant.
I don't know how FI drag compares to actual failed engine/windmilling prop drag but the platform I fly also performs with one engine at FI, obviously not as well as when feathered or with zero thrust set but a very definite positive gradient nonetheless.
I think I agree with FGD though, I don't think FI would replicate a completely failed powerplant with a pitchlocked prop. One aircraft I have flown (in a sim) without autofeathering could only climb briefly before starting a gradual descent.