This question reminds me of some cultivation or isekai stories where an underestimated protagonist ends up with multiple powerful partners. The growth often hinges on the tension between his perceived weakness and the hidden potential the goddesses see or unlock in him. He's not just an idiot; there's usually a system, a secret heritage, or a profound innocence that allows him to bypass political scheming others are mired in. His 'foolishness' can be a shield, letting him form genuine bonds where a cunning lord would fail.
In many narratives, the wives themselves become the catalysts. Each goddess, representing a different domain like war, wisdom, or healing, challenges and nurtures a specific aspect of him. The growth is less about brute power and more about emotional and social intelligence—learning to trust, delegate, and lead through unity rather than fear. The comedy or drama comes from him stumbling into solutions that his 'smarter' enemies would never consider, turning his greatest flaw into his most unpredictable strength.
A series like 'The Genius Assassin' plays with this, though the MC there is cunning. For a true 'imbecile' lord, his arc might involve discovering that his simple, direct honesty is the very thing that stabilizes the chaotic divine household, making the goddesses, for all their power, choose to protect and elevate him. The ending feels earned when his naive perspective solves a crisis the goddesses' complex approaches couldn't.