If your through hulls are manganese bronze I would be surprised. All good quality bronze through hulls I know of (Groco, Apollo/Conbraco) are 85-5-5-5 bronze which has 5% zinc. I believe it needs to be 10% zinc to have dezincification issues. There is, in my opinion, no advantage to bonding through hulls. Stan Honey gives reasons here: Grounding
Bonding a through hull that is isolated and all of one metal in composition is only inviting it to have issues.
Your prop is probably manganese bronze which contains up to 39% zinc and does need galvanic protection.