Desmotronic, all 3-blade B200s and McCauley 4-blade B200s are certified for Vmca with a windmilling prop.
Hartzell-Raytheon and Hartzell-Raisbeck 4-blade B200s are certified with the inop feathered. That's why on these machines AFX is a mandatory system. If it doesn't work you don't take off.
Yes if you pull a power lever back when AFX is doing its thing you'll disarm the system. That's why the checklist does not direct you to pull back a power lever for an engine failure after takeoff/in flight. And they also have a note at the bottom of that checklist about the AFX being disarmed if you do.