I see your point, but I think it more proves my point.
The janitor in your scenario represent the polygynist, in my mind. The janitor has intimate, committed, working knowledge of that building. He knows its ins and outs. It’s workings, deficiencies and needs. He’s the expert for that building. Outside knowledge of systems in general is fine, but are not specific to that particular building.
I prefer the expert input of someone who has an intimate understanding of polygyny, having lived it. Someone who has “...in like manner, dwelt with his wives according to knowledge (gnosis)...”. His lived experience may not translate to my life, but I personally value it more than any other type of knowledge.