But it is the surveyor who maybe was misguided writes down ABYC regulations that are newer, never before applied to an older boat that an insurance agent treats as gospel and demands be rectified before full endorsement is given.
On the other hand, some surveyors may not be up to date or they use common sense and not write down some obvious ABYC suggestions.
It is easier for insurance agents to err on the side of caution.
That's all part of an insurance company deciding if they want to write a policy in the first place, and I agree it's very problematic.
I can guarantee that any older boat doesn't meet all current ABYC standards, and I don't think any insurance company expects them too. The question then is what aspects of the boat SHOULD be updated for the risk to be acceptable to the insurance company. Maybe others know, but I'm not aware of any guidelines that insurance companies give to surveyors telling them what areas they want to be up to date. I think it's all left to the surveyor. I think it's critical for any boat owner to have a very frank discussion with a prospective surveyor about the purpose of the survey, and even discuss the sorts of things the surveyor will call out as requiring an update.
If you are getting a pre-purchase survey, I think you want to know everything, and get every suggestion and recommendation the surveyor has. It's then up to you to decide what you are going to fix/update, and in what priority order. But for an insurance survey, I think you only want the items that make the boat a danger or poor risk.
Electrical stuff is probably one of the biggest risks on a boat, so I can understand insurance companies wanting certain base standards met. RCD might be long hanging fruit with a lot of risk reduction for little cost. Ancient propane installations are probably another one.
All these things are judgement calls, and I think the best thing an owner can do is have a frank discussion with prospective surveyor about the purpose of the survey, and ans blunt questions about how they arrive at recommendations.
As for this specific question about RCDs, I'd probably go back to the surveyor with the ABYC language, ask if they agree, and see if they will ammend the survey. If not, you could take it up with the insurance company showing them that the surveyor erred in their recommendation. Or just install an RCD and move on.