I doubt I will be able to get enough force into my swing to get him to let go of me.
Exactly.
Long ago while a student in martial arts I remember being taught to advance in the face of a bat, stick, 5cell mag lite, etc. For the above reason. In addition an overhead strike can easily be block without severe damage by merely angling your arm causing the force to glance down your blocking arm distributing or cushioning it. Slight movement on the part of the hit-tee can cause your strike to miss the mark also. Once you have missed then you are extremely vulnerable.
Capt Charlie, If I knew in advance that I would be able to get in a head blow to each bad guy then I would agree with the maglite. If direct hits are achieved with both weapons the 5cell will stop the fight faster. It is just harder to get that "direct" hit with the maglite.
One thing is certain, they don't want to get into cutting distance of me with a knife.