With all due respect, I don't know who you are insured with, but my experience is that insurers have not charged more for racers in decades.
I have 2 policies, one with Boat/US and one with Progressive. The application for my Boat/US policy in the "WHERE" Section asks "Is Boat used for Racing?"..."If Yes, approximate % of racing"..."Types of races..." The Boat/US policy does not exclude sailboat racing from coverage (but does exclude powerboat racing), but that does not mean it does not charge a premium for it in underwriting. A Google search will reveal some threads where sailboat owners have experienced a surcharge for racing, or a denial of coverage.
My Progressive policy excludes the following: "4. bodily injury or property damage resulting from, or sustained during practice or preparation for: (a). any pre-arranged or organized racing, stunting, speed, or demolition contest or activity;..."
The other clause an insurance company may try to use to deny coverage is the standard provision excluding activities in which you assume the risk, which a racer does when signing up for a race through the organizing body.
All questions on insurance applications are relevant to underwriting, risk assessment, and risk allocation. If, for instance, someone does race, but does not reveal it on the application, that would be a basis for denying a claim.
My experience in the insurance area leads me to believe most folks do not read or understand their insurance policies, and rely on their agent, a saleperson who does not evaluate claims, for information. The legal field is ripe with litigation over claims coverage and denial, and many folks are not entirely honest in applying for insurance, thinking a little fudging wouldn't come back to bite them later.
While I would agree that racers are generally more skilled in handling their boats than cruisers, racing does expose a boat to additional risks. I suspect the precise issue is not often addressed, because of fudging and paying for damages out of pocket.
You should have received a discount when your risk was decreased by not racing. I would not rely on the oral statements of one underwriter. It may be that your particular boat model is frequently used for racing, has higher claims as a result, and therefore the additional premium is built into your boat type. That would not be true for a Catalina 36.