I have to agree with your assessment. I can see how Doc's ProPlugs might be useful for preventing swimmer's ear (infection of the outer ear) or in the case that someone wanted to dive with a torn/damaged eardrum (not a good idea IMO). For preventing middle ear barotrauma, I honestly don't see how the ProPlugs could help. In fact, if the small hole, through which equalization occurs, gets plugged for some reason (earwax?), then the product is going to hinder ear equalization.
I have not used ProPlugs, but I have looked into how they are supposed to work.