It doesn't make sense to me, that the engine would perform fine in sea trials and then suddenly start loping and running poorly after "just" fuel polishing. Which shouldn't affect the engine at all.
Whether the surveyor was right to just listen to the engine, or to do something more invasive (using a borescope, as the Yanmar dealer did) is a good question. Many owners would have no idea about the engine ingesting some sea water, and without a specific engine mechanic's survey, most general surveys will not look any further than "how does the engine sound".
You'd probably have a 50-50 chance of recovering against either one of them, flip of a coin and the written terms of the survey to decide the details.
"He said that he saw no need for a compression check since the engine started right away. " Then again, an engine will start nice and fast when there's a little LESS compression, so the starter can spin it up real fast. And, something like carbon deposits (or calcium) would serve to BOOST the compression...so the surveyor's statement on this would seem totally illogical.