As a 30+ year veteran, damn i'm old, of the insurance industry I read this entire post with great interest and honestly a bit of angst.
In my opinion most important and accurate points have been hit on
-Insurance companies like USAA partner with other carriers to offer products, i.e. yacht or perhaps actually watercraft policies as they do not see the necessary return to insure themselves. Keep in mind yacht insurance is a specialized game , yes most of us own boats that would be considered yachts in the insurance world.
-While it may appear that USAA is looking to sell Progressive policies to gain commission income I can say from experience, I have been directly involved in similar relationships, it has much less to do with commission than serving their members. Please don't stop reading and allow me to explain. In the insurance world there is something known as a switching cost, meaning the more painful it is for an insured to leave and go to a new company the greater a chance you will stay with the company, simply put its a pain to move my home, auto, boat, life..... policies. It's all about retaining you as their customer.
-USAA is a top notch carrier, there is not a single measure in the Insurance Industry that most companies are envious of: as, I work for a Direct competitor.
-So what to do, well the entire USAA program came about as desire to meet the needs of their members so you can petition USAA to add a true yacht carrier to their fold of partners, but my guess is they may not have the necessary return as the more cookie cutter nature of auto insurance does not transfer over into the Yacht/Watercraft world.
-I will go back to Peggy Halls early counsel. Find a yacht insurance broker that can shop multiple companies for the one that meets both your insurance and budget needs. While they are specialized brokers they are not rare, we have several within a short ride from my marina on Long Island Sound. Anyone in a coastal state or on the Great Lakes should be able to find several local as well as a plethora of reputable national brokers .
The most important thing I wanted to share is Yacht insurance is not Auto Insurance, there is a host of very unique exposures in the yachting world I would not trust your average call center agent to understand, for example what coverage does your policy have for pollution if your trusty Yanmar starts spitting oil into the wetlands or say what is the duty of the insurer to defend you from a friendly commercial captain who comes to your aid in an emergency then attempts to take ownership of your vessel based on Maritime Salvage Laws?
My opinion/advice the complexities of the insurance most of us need simply cannot be provided by a carrier or broker that does not specialize in it. I encourage you to take the extra time, its really not that much more time, to get the advice you need from people that are competent in yacht insurance as the last thing you want is to find you have the wrong coverage after you have a loss.
Good Luck